## Seismic Design With Base Isolation

## Seismic Isolation for Designers and Structural Engineers

This book provides both theory and design aspects of seismic isolation. This will be useful for structural engineers and teachers of engineering courses. For other structural components (concrete frames, steel braces etc) the. engineering student is taught the theory (lateral loads, bending moments) but then also the design (how to select sizes, detail reinforcing, bolts). This book will do the same for seismic engineering. The book provides practical examples of computer applications as well as device design examples so that the. structural engineer is able to do a preliminary design that wont specify impossible constraints. The book also addresses the steps that need to be taken to ensure the design is code-compliant.

#### Seismic Isolation for Designers and Structural Engineers Summary

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## Manual For Seismic Design Afps

Chen W-F. and Scawthorn C. (2003) (editors) Earthquake engineering handbook. Press, oca aton F . Hamburger R. and Nazir N. (2003) Seismic design of steel structures. In Chen and Scawthorn (editors), Earthquake engineering handbook. CRC Press, Boca Raton FA. ISE AFPS (2009) Manual for the seismic design of steel and concrete buildings to Eurocode 8. Institution of Structural Engineers, London. Taranath B. S. (1998) Steel, concrete and composite design of tall buildings. McGraw-Hill, NY.

## Reliabilitybased Seismic Design

There are a number of ways to quantify the seismic performance of a building, the form of which should be dictated by both structural engineers and building owners. As discussed in Chapter 2, performance-based seismic design requires the selection of performance objectives that consist of a level of performance coupled with a level of earthquake ground motion. The performance objective for a building can be quantified in terms of a performance Junction,

## Performance Based Seismic Design

The objective of Performance-Based Seismic Design (PBSD) is to accurately predict, in definable terms, the performance of a building during any intensity of earthquake ground motion that may occur at the building site over the lifetime, or design life, of the building. Definable performance can be accomplished by designing the building to meet a wide range of performance objectives. A single performance objective New buildings designed in accordance with current design standards satisfy a limited set of performance objectives. The 1996 Structural Engineers Association of California (SEAOC) Recommended Lateral Force Requirements and Commentary (SEAOC, 1996), also known as the 1996 SEAOC Blue Book, requires buildings to be designed to meet only a single performance objective. The earthquake hazard is quantified as the ground motion that occurs once every 475 years, i.e. 10 probability of exceedance in 50 years. For this level of earthquake hazard, the objective of the building design is...

## Performancebased Seismic Design

This chapter provides a description of the Performance-Based Seismic Design methodology and the state-of-the-art guidelines and code provisions for the design of new buildings and the rehabilitation of existing buildings. Section 2.2 describes the Performance-Based Seismic Design methodology. Section 2.3 describes the state-of-the-art guidelines and code provisions for the design of new buildings. Section 2.4 describes the state-of-the-art recommended guidelines for the rehabilitation of existing buildings. Current performance-based design guidelines and acceptance criteria for steel moment frame buildings are discussed in Section 2.5.

## Code Procedure for Seismic Design Category A

Structures determined to be in Seismic Design Category (SDC) A are required to comply only with the provisions of Section 1616.4 1 . There are five exceptions to this rule. First, detached Group R-3 dwellings in SDC A, B, and C are exempt from the general seismic provisions. Detached one- and two-family dwellings and multiple single-family dwellings (townhouses) not more than three stories high with separate means of egress and their accessory structures shall comply with the International Residential Code (IBC 101.2). Second, wood frame seismic resisting systems need only conform to the provisions of Section 2308 (Conventional Light-Frame Construction). Third, agricultural storage structures intended only for incidental human occupancy do not need to be designed for seismic forces. Fourth, structures where Ss < .15g and S, < .04g need only comply with Section 1616.4. Similarly, structures where SDS < .167gand SDI < .067g need only comply with Section 1616.4 1 . The Simplified...

## Standardisation of seismic design

The appearance of displacement-based analysis methods makes it possible to foresee an evolution towards a fourth generation of seismic design codes, where the various components of the seismic behaviour will be better controlled, in particular those that relate to energy dissipation. Fro this point of view, in its present configuration, EC 8 is at the junction bettveen the third generation codes, of which it still forms part, and of fourth generation codes.

## Introduction To Euro 8 Seismic Design

In line with current seismic design practice, steel structures may be designed to EC8 according to either non-dissipative or dissipative behaviour. The former, through which the structure is dimensioned to respond largely in the elastic range, is normally limited to areas of low seismicity or to structures of special use and importance it may also be feasible if vibration reduction devices are incorporated. Otherwise, codes aim to achieve economical design by employing dissipative behaviour in which considerable inelastic deformations can be accommodated under significant seismic events. In the case of irregular or complex structures, detailed non-linear dynamic analysis may be necessary. However, dissipative design of regular structures is usually performed by assigning a structural behaviour factor (i.e. force reduction or modification factor) that is used to reduce the code-specified forces resulting fro idealised elastic response spectra. his is carried out in conjunction ith the...

## Eurocode Gusset Plate Connection

Astaneh, A. (1995) Seismic design of bolted steel moment resisting frames, Structural Steel Educational Council, July, 82 pp. Castro, J. M., Davila-Arbona, F. J. and Elghazouli, A. Y. (2008) Seismic design approaches for panel zones in steel moment frames, Journal of Earthquake Engineering, 12(S1), 34-51. EERI (1995) The Hyogo-ken Nanbu Earthquake Preliminary Reconnaissance Report, Earthquake Engineering Research Institute Report no. 95-04, 116 pp. Elghazouli, A. Y. (1996) Ductility of frames with semi-rigid connections, 11th World Conf. on Earthquake Engineering, Acapulco, Mexico, Paper No. 1126. Elghazouli, A. Y. (1999) Seismic Design of Steel Structures, SECED-Imperial College Short Course on Practical Seismic Design for New and Existing Structures, Imperial College, London. Elghazouli, A. Y. (2003) Seismic design procedures for concentrically braced frames, Proceedings of the Institution of Civil Engineers, Structures and Buildings, 156, 381-394. Elghazouli, A. Y. (2007) Seismic...

## Design example concentrically braced frame Introduction

The same eight-storey building considered previously is utilised in this example. The main seismic design checks are carried out for a preliminary design according to EN 1998-1. For the purpose of illustrating the checks in a simple manner, consideration is only given to the lateral system in the X-direction of the plan, in which resistance is assumed to be provided by concentrically braced frames spaced at 8 m. With reference to the plan shown before in Figure 6.17, eight braced frames are considered at Grid lines 1, 3, 5, 7, 9, 11, 13 and 15. It is also assumed that an independent bracing system is provided in the transverse Qf) direction of the plan. Grade S275 is considered for the structural steel used in the example. 6.9.3 Seismic design checks 6.9.3.1 General considerations

## Design example on a pile foundation

In this section e shall outline the design of a pile foundation for a typical column of the building for which the seismic designs were carried out in earlier chapters. f course in reality the design of pile foundations ill be carried out for individual columns with the associated reductions in the pile lengths and or pile diameters to suit the design load on the column. Here we shall only consider one typical column along the D line on the plan of the building.

## Pile Foundation Failure

Eotechnical engineers are called upon to design deep foundations hen the shallo layers of soils beneath the building are either unable to support the loads iposed by the superstructure on the shallo foundations or if the shallow layers may become unstable due to the cyclic shear stresses induced by the earthquake loading. Under such circumstances it is imperative to look for pile foundations that transfer the load fro the superstructure to ore fir and stable soil strata at deeper levels or onto bedrock. In this chapter the seismic design of pile foundations is considered in the light of the EC 8 Part 5 (2003) provisions as well as some of the current research findings. It is perhaps helpful if some of the well-known examples of failures of pile foundations during or following an earthquake loading are considered first.

## Elastic design response spectra

Most seismic design is based on representing the earthquake actions in the for of an equivalent static force applied to the structure. hese forces are determined from the maximum acceleration response of the structure under the expected earthquake-induced ground shaking, hich is represented by the acceleration response spectrum. The starting point is an elastic response spectrum, which is subsequently reduced by factors that account for the capacity of the structure to dissipate the seismic energy through inelastic deformations. The definition of the elastic response spectrum and its conversion to an inelastic spectrum are presented in Chapter 3 this section focuses on how the elastic design response spectra are presented in seismic design codes, with particular reference to EC8. The purpose of representing earthquake actions in a seismic design code such as EC8 is to circumvent the necessity of carrying out a site-specific seismic hazard analysis for every engineering project in...

## Overview of this book

Seismic design of structures aims at ensuring, in the event of occurrence of a reference earthquake, the protection of human lives, the Imitation of damage to the structures, and operational continuity of constructions important for civil safety. These goals are linked to seismic actions. Chapter 2 of this book provides a detailed review of methods used in determining seismic hazards and earthquake actions. It covers seismicity and ground-motion models, with specific reference to the stipulations of EC8. In the illustrative design examples presented in Chapters 3 through to 9 of this book, reference is made to the relevant rules and clauses in EC8, such that the discussions and calculations can be considered in conjunction with the code procedures. To this end, it is important to note that this publication is not intended as a complete description of the code requirements or as a replacement for any of its provisions. The purpose of this book is mainly to provide background...

## Booth and Z Lubkowski

EC8 Part 1 Section 4.2.1 sets out some aspects of seismic design specifically for buildings, which should be considered at conceptual design stage, and which will assist in meeting the 'no collapse' and 'damage limitation' requirements. It is not mandatory that they should be satisfied, and indeed since they are qualitative in nature, it would be hard to enforce them, but they are sound principles that deserve study. Related, but quantified, rules generally appear elsewhere in EC8 for example, the structural regularity rules in Section 4.2.3 supplement the uniformity and symmetry principles given in Section 4.2.1. Six guiding principles are given EC8 Part 1 Section he interaction of foundations ith the ground, in addition to interaction with the superstructure, is of course vital to seismic performance. Part 5 of EC8 gives related advice on conceptual seismic design of foundations, and this is further discussed in hapters 8 and 9. Seismic isolation involves the introduction of low...

## Conclusions and recommendations

Most frequently be obtained through probabilistic seismic hazard analysis, which provides the most rational framework for handling the large uncertainties associated with the models for seismicity and ground-motion prediction. Most seismic design codes present zonation maps and response spectra derived probabilistically, even though these design loads are often associated ith a return period hose origin is a fairly arbitrary selection, and the resulting response spectrum is generally a poor approximation to the concept of a uniform hazard spectrum. EC8 is unique amongst seismic design codes in that it is actually a template for a code rather than a complete set of definitions of earthquake actions for engineering design. Each member state of the European Union will have to produce its own National Application Document, including a seismic hazard map showing PGA values for the 475-year return period, select either the Type 1 or Type 2 spectrum and, if considered appropriate, adapt...

## Design For Dcm And

EC8 (2004) Eurocode 8 Design of structures for earthquake resistance. General rules, seismic actions and rules for buildings. EN 1998-1 2004, European Committee for Standardization, russels. Fajfar P. (2002) Structural analysis in earthquake engineering - a breakthrough of simplified non-linear methods. Proc. 12th European Conf. on Earthquake Engineering, London, Elsevier, Paper 843. Hitchings D. (1992) A Finite Element Dynamics Primer, NAFEMS, London. Krawinkler H., Seneviratna G. (1998) Pros and cons of a pushover analysis for seismic performance evaluation. Eng. Struct., 20, 452-464. Lawson R.S., Vance V, Krawinkler H. (1994) Nonlinear static pushover analysis -why, when and how Proc. 5th US Conf. on Earthquake Engineering, Chicago IL, Vol. 1, 283-292.

## Design example moment frame Introduction

The same eight-storey building considered in previous chapters is utilised in this example. The layout of the structure is reproduced in Figure 6.17. The main seismic design checks are carried out for a preliminary design according to EN 1998-1. For the purpose of illustrating the main seismic checks in a simple manner, consideration is only given to the lateral system in the X-direction of the plan, in which resistance is assumed to be provided by MRFs spaced at 4 m. It is also assumed that an independent bracing system is provided in the transverse (Y) direction of the plan. Grade S275 is assumed for the structural steel used in the example.

## Acceleration timehistories

Although seismic design invariably begins with methods of analysis in which the earthquake actions are represented in the form of response spectra, some situations require fully dynamic analyses to be performed and in these cases the earthquake actions ust be represented in the for of acceleration time-histories. Such situations include the design of safety-critical structures, highly irregular buildings, base-isolated structures, and structures designed for a high degree of ductility. For such projects, the simulation of structural response using a scaled elastic response spectrum is not considered appropriate and suites of accelerograms are required for the dynamic analyses. The guidance given in the majority of seismic design codes on the selection and There are a number of options for obtaining suites of acceleration time-histories for dynamic analysis of structures, including the generation of spectrum-compatible accelerograms from white noise, a method that is no idely regarded...

## Pappin 1991 Design Of Foundation And Soil Structures For Seismic Loading

Ambraseys, N.N. and Menu, J.M. (1988) Earthquake-induced ground displacements. Earthquake Engineering & Structural Dynamics, 16, 985-1006. Auvinet, G., Pecker, A. and Salenjon, J. (1996) Seismic bearing capacity of shallow foundations in Mexico City during the 1985 Michoacan earthquake. Proceedings of the 11th World Conference on Earthquake Engineering, Acapulco. Finn, L., Iai, S. and Matsunaga, Y (1995) The effects of site conditions on ground motions. Tenth European Conference Earthquake Engineering, Duma, G. (ed.), Balkema, Rotterdam. Lysmer, J., Udaka, T., Tsai, C-F. and Seed, H.B. (1975) FLUSH - a computer program for approximate 3-D analysis of soil-structure interaction problems, Report No. UCB EERC-75 30, Earthquake Engineering Research Center, University of alifornia, erkeley. Mohammadioun, B. and Pecker, A. (1984) Low frequency transfer of seismic energy by superficial soil deposits and soft rocks. Earthquake Engineering and Structural Dynamics, 12, 537-564. Pecker, A....

## Dogbone Eccentrically Braced Frames

Where the actions are similar to those previously defined for concentrically braced frames. However, in this case W is the minimum of the following (i) min of W. 1-5VpUnkj VEdj among all short links, and (ii) min of W. 1.5MpUnkj MEdj among all intermediate and long links where VEdi and MEdj are the design values of the shear force and bending moment in link 'i' in the seismic design situation, whilst Vp link. and Mp ink. are the shear and bending plastic design capacities, respectively, of link i. It should also be checked that the individual values of W. do not differ from the minimum value by more than 25 per cent in order to ensure reasonable distribution of ductility.

## Groundmotion characterisation and prediction

The crux of specifying earthquake actions for seismic design lies in estimating the ground otions caused by earthquakes. he inertial loads that are ultimately induced in structures are directly related to the motion of the ground upon hich the structure is built. he present section is concerned with introducing the tools developed, and used, by engineering seismologists for the purpose of relating hat occurs at the source of an earthquake to the ground otions that can be expected at any given site.

## Implementation of EC in Member States

O allo the application of E8 in a given territory, it is necessary to have a seismic zoning map and associated data defining peak ground accelerations and spectral shapes. his set of data, hich constitutes an essential basis for analysis, can be directly introduced into the National Annex. However, in certain countries, seismic design codes are regulated by statute and, where this applies, zoning aps and associated data are defined separately by the national authorities.

## Strength verification

Aving derived the design shear and bending actions in the structural members, the resistances are then calculated according to EC2. If the partial material factors are chosen as discussed in Section 5.2.4 to cater for potential strength degradation, then the design process is simplified. Standard design aids for strength such as Narayanan and Beeby (2005) or guidance available on the Internet (e.g. www.concretecentre.com) can then be used for seismic design. However, EC8 allows National Authorities to choose more complex options.

## Contents of EC

EC8 comprises six parts relating to different types of structures (Table 1.1). Parts 1 and 5 form the basis for the seismic design of new buildings and their foundations their rules are aimed both at protecting human life and also limiting economic loss. It is interesting to note that EC 8 Part 1 also provides design rules for base isolated structures.

## Capacity Design

Whilst capacity design is an important concept for seismic design in all aterials, it is included here because it is particularly relevant to reinforced concrete structures, hich can potentially exhibit brittle failure odes unless attention is paid to suppressing these odes in the design and detailing.

## D The Use Of Eurocode Outside The Uk Dll Introduction

Considerable interest in Eurocode 7 is being expressed in many parts of the world for example, 26 countries were represented at a Seminar held by the Institution of Structural Engineers in 1996 (Orr (1996)). Attitudes to the Eurocode, at least in the Member States of the EU, may be differentiated roughly by geographic location. The Scandinavian countries have, by and large, more readily accepted the use of partial factor design, reflecting perhaps the influences of Brinch Hansen in the region. Indeed, in Denmark, their national codes, embodying partial factor design, are well advanced. Other 'northern' European countries such as France, Germany and the UK, having in place comprehensive, well-tried sets of geotechnical codes and standards based heavily on empiricism, have been less ready to embrace partial factors. The southern European countries generally have less comprehensive codes and rely to a greater extent on legislation and government to implement safety regulations.

## PfH F pxlxaxlldxdxdxll

Typically, structural engineers use approximate models because they are a convenient way to predict a building performance quantity by making simplifying assumptions about the true effects and interactions of basic variables. The use of a linear response spectrum analysis instead of a nonlinear time history analysis to estimate the maximum interstory drift demand on a building is an example of such a modeling decision that results in modeling uncertainty. Another source of modeling uncertainty is the statistical uncertainty resulting from the use of a limited number of samples to calculate the central value and dispersion in a building performance quantity. For example, if a nonlinear time history analysis is used to estimate building response to earthquake ground motions, then a single earthquake ground motion sample will result in an estimate of the maximum interstory drift As the number of earthquake ground motion samples increases, the knowledge...

## Global and local ductility through capacity design and member detailing overview

Further to the control of the global inelastic response mechanism through selection of the structural configuration and dimensioning of vertical members to remain elastic above the base, the design strategy aims at ensuring that those individual members where the demand for global ductility and energy dissipation is spread possess the necessary local capacity to sustain this demand. As concrete members can dissipate energy and develop significant cyclic ductility only in flexure - and this only if certain conditions on material ductility and detailing are met - failure of members in shear before they yield in flexure should be precluded. To this end, prevention of pre-emptive shear failure is pursued by establishing the shear force demands on primary seismic beams, columns and walls in DCM and DCH buildings and beam-column joints in DCH frames not from the analysis for the seismic design situation but through capacity design calculations, as outlined in Section 5.6.4. In addition, the...

## Energy dissipation capacity and ductility classes

(1)P The design of earthquake resistant concrete buildings shall provide the structure with an adequate capacity to dissipate energy without substantial reduction of its overall resistance against horizontal and vertical loading. To this end, the requirements and criteria of Section 2 apply. In the seismic design situation adequate resistance of all structural elements shall be provided, and non-linear deformation demands in critical regions should be commensurate with the overall ductility assumed in calculations. (2)P Concrete buildings may alternatively be designed for low dissipation capacity and low ductility, by applying only the rules of EN 1992-1-1 2004 for the seismic design situation, and neglecting the specific provisions given in this section, provided the requirements set forth in 5.3 are met. For buildings which are not base-isolated (see Section 10), design with this alternative, termed ductility class L (low), is recommended only in low seismicity cases (see 3.2.1(4)).

## Combination for local effects

At the local level, i.e. for the verification of members and sections, the design seismic action is combined with other actions as specified in EN 19903 for the seismic design situation. Symbolically, this combination is X< Jk '+'AEi'+' Qk, ,> where Gk is the nominal value of permanent action j (normally the self weight and all other dead loads), AE is the design seismic action (corresponding to the 'reference return period' multiplied by the importance factor), QKj is the nominal value of variable action i (live loads (in Eurocode terminology 'imposed loads') wind, snow load, temperature, etc.) and tp2, Q , is the quasi-permanent (i.e. the arbitrary-point-in-time) value of variable action i. Being quasi-permanent, the action effects of 4> 2JQ i are taken into account always, regardless of whether they are locally favourable or unfavourable. If the same value of ip2J applies to all storeys, this is very convenient for the design, as it lends itself to a single analysis for the...

## Bending and shear resistance

(1)P Flexural and shear resistances shall be computed in accordance with EN 1992-11 2004, unless specified otherwise in the following paragraphs, using the value of the axial force resulting from the analysis in the seismic design situation. (2) At the critical regions of walls a value of the curvature ductility factor should be provided, that is at least equal to that calculated from expressions (5.4), (5.5) in 5.2.3.4(3) with the basic value of the behaviour factor qo in these expressions replaced by the product of qo times the maximum value of the ratio MEd MRd at the base of the wall in the seismic design situation, where MEd is the design bending moment from the analysis and MRd is the design flexural resistance. (11) In the height of the wall above the critical region only the relevant rules of EN 1992-1-1 2004 regarding vertical, horizontal and transverse reinforcement apply. However, in those parts of the section where under the seismic design situation the compressive strain...

## The lateral force method of analysis

In the lateral force method a linear static analysis of the structure is performed under a set of lateral forces applied separately in two orthogonal horizontal directions, X and Y. The intent is to simulate through these forces the peak inertia loads induced by the horizontal component of the seismic action in the two directions, X or Y. Owing to the familiarity and experience of structural engineers with elastic analysis for static loads (due to gravity, wind or other static actions), this method has long been - and still is - the workhorse for practical seismic design. The version of the method in Eurocode 8 has been tuned to give similar results for storey shears - considered as the fundamental seismic action effects - as those from modal response spectrum analysis (which is the reference method), at least for the type of structures to which the lateral force method is considered applicable. As the use of modal response spectrum analysis is not subject to any constraints of...

## Modal response spectrum analysis

Modal analysis and its results Clause 4.3.3.3 Unlike linear static analysis, designers may not be so familiar with linear dynamic analysis of the modal response spectrum type. Moreover, some commercial computer programs with modal response spectrum analysis capability may not perform such an analysis in accordance with the relevant requirements of Eurocode 8. For instance, along the line of other seismic design codes (e.g. some US codes), a program may use the modal response spectrum method just to estimate peak inertia forces at storey levels, and to then apply these forces as static forces and calculate the static response to them as in the lateral force method. For these reasons, an overview is given below of how modal response spectrum analysis should be performed to fulfil the letter and spirit of EN 1998-1. The most commonly used criterion, requiring a sum of effective modal masses along each individual seismic action component, X, Y or Z, considered in design, of at...

## Behaviour factor q of concrete buildings designed for energy dissipation

Seismic action and for the gravity loads included in the load combination of the seismic design situation. The value of au may be found as the ratio of the base shear on development of a full plastic mechanism according to a pushover analysis to the base shear due to the design seismic action (Fig. 5.2). Gravity loads considered to act simultaneously with the seismic action should be maintained constant in the pushover analysis, while lateral forces increase. For consistency with the calculation of av the moment capacities at member ends in the pushover analysis should be the design values, MRd. If the mean values of moment capacities are used instead, as customary in pushover analysis, the same values should also be used for the calculation of av

## Elevation Regularity Eurocode

As in most other modern seismic design codes, the concept of building regularity in EN 1998-1 is presented with a separation between regularity in plan and regularity in elevation. Moreover, regularity in elevation is considered separately in the two orthogonal directions in which the horizontal components of the seismic action are applied, meaning that the structural system may be characterized as regular in one of these two horizontal directions but not in the other. However, a building assumes a single characterization for regularity in plan, independent of direction. Unlike US codes (e.g. see Building Seismic Safety Council39 and Structural Engineers Association of California40), which set quantitative - albeit arbitrary - criteria for regularity

## Definition and role of primary and secondary seismic elements

Seismic', as far as their role and contribution to earthquake resistance of the building is concerned. The main objective of this distinction is to allow for some simplification of the seismic design by not considering such elements in the structural model used for the seismic analysis of the building. Accordingly, only the remaining elements, which are termed 'primary seismic members', should be modelled in the structural analysis and designed and detailed for earthquake resistance in full accordance with the rules of Sections 5-9 in EN 1998-1. The differentiation between primary and secondary elements is essentially equivalent to the traditional distinction in US seismic design codes for new buildings between members which belong to the lateral-force-resisting system and those that do not. The terminology of primary and secondary elements has also been adopted by the US prestandard for seismic retrofitting of existing buildings.45,46 In EN 1998-1, the term 'seismic' has been added...

## Detailing for local ductility

(1)P The regions of a primary seismic beam up to a distance lcr hw (where hw denotes the depth of the beam) from an end cross-section where the beam frames into a beam-column joint, as well as from both sides of any other cross-section liable to yield in the seismic design situation, shall be considered as being critical regions. a) at the compression zone reinforcement of not less than half of the reinforcement provided at the tension zone is placed, in addition to any compression reinforcement needed for the ULS verification of the beam in the seismic design situation. (1)P Flexural and shear resistance shall be computed in accordance with EN 1992-11 2004, using the value of the axial force from the analysis in the seismic design situation. (12)P The transverse reinforcement within the critical region at the base of the primary seismic columns may be determined as specified in EN 1992-1-1 2004, provided that the value of the normalised axial load in the seismic design situation is...

## Introduction and scope

If the contribution of masonry infills to the lateral strength and stiffness of the building is large relative to that of the structure itself, the infills may override the seismic design of the structure and invalidate both the efforts of the designer and the intention of Eurocode 8 to control the inelastic response by spreading the inelastic deformation demands throughout the structure and the building. For instance, loss of integrity of ground storey infills will produce a soft storey there, and may trigger collapse of the structural frame itself. Concentration of inelastic deformation demands in a small part of the building is much more likely if the infills are not uniformly distributed in plan or - more importantly - in elevation. This situation may also have serious adverse effects on seismic performance and safety. Last

## Structural types and behaviour factors Structural types

(3)P A wall system shall be classified as a system of large lightly reinforced walls if, in the horizontal direction of interest, it comprises at least two walls with a horizontal dimension of not less than 4,0 m or 2hw 3, whichever is less, which collectively support at least 20 of the total gravity load from above in the seismic design situation, and has a fundamental period T1, for assumed fixity at the base against rotation, less than or equal to 0,5 s. It is sufficient to have only one wall meeting the above conditions in one of the two directions, provided that (a) the basic value of the behaviour factor, qo, in that direction is divided by a factor of 1,5 over the value given in Table 5.1 and (b) that there are at least two walls meeting the above conditions in the orthogonal direction.

## Concrete foundation elements Scope

(2)P If design action effects for the design of foundation elements of dissipative structures are derived on the basis of capacity design considerations in accordance with 4.4.2.6(2)P, no energy dissipation is expected in these elements in the seismic design situation. The design of these elements may follow the rules of 5.3.2(1)P. (3)P If design action effects for foundation elements of dissipative structures are derived on the basis of the analysis for the seismic design situation without the capacity design considerations of 4.4.2.6(2)P, the design of these elements shall follow the corresponding rules for elements of the superstructure for the selected ductility class. For tie-beams and foundation beams the design shear forces need to be derived on the basis of capacity design considerations, in accordance with 5.4.2.2 in DCM buildings, or to 5.5.2.1(2)P, 5.5.2.1(3) in DCH buildings. (5) In box-type basements of dissipative structures, comprising a) a concrete slab acting as a...

## Dimensioning for the ULS in bending with axial force

Moments above the base over those obtained from the analysis for the seismic design 5.4.3.5.1(1), ground. Such hard impacts excite high-frequency vertical vibrations of the whole of the large wall, or of certain storeys of it. Being of high frequency, these vibrations die out fast and do not have significant global effects. However, they may induce significant fluctuation of the axial force in each individual wall. In view of the inherent uncertainty and the complexity of the local phenomena, Section 5 allows taking into account this fluctuation in a simplified and safe-sided way, namely by increasing or decreasing the design axial force of each individual wall by half its axial force due to the gravity loads present in the seismic design situation. It also allows neglecting this additional force if the value of the q factor used in the design does not exceed the value q 2. The vertical reinforcement is normally conditioned by the case in which the additional axial force is taken in...

## Design and detailing of foundation elements

Due to the high rigidity and strength of a box-type foundation system, that part of the columns within its height, as well as all beams within the foundation system (including those at the roof of the basement), are expected to remain elastic in the seismic design situation and hence may follow the simpler dimensioning and detailing rules applying to DCL (i.e. those of Eurocode 2 alone, plus the requirement to use steel of at least Class B), irrespective of the ductility class for which the building is designed. Tie beams between footings and tie zones in foundation slabs should be dimensioned for the ULS in shear and in bending for the action effects determined from the analysis for the seismic design situation or via capacity design calculations, and to a simultaneously acting axial force (tensile or compressive, whichever is more unfavourable) equal to a fraction of the mean value of the design axial forces of the connected vertical elements in the seismic design situation. This...

## Ductile walls coupled and uncoupled

Because in coupled walls more energy is normally dissipated in the coupling beams than in the plastic hinges at the base of the individual walls, the coupling beams are equally important as these walls, and Section 5 has special dimensioning and detailing provisions for them. (In fact, the couple moment of the axial forces in the individual walls, on which a lower limit of 25 of the total bending moment of the individual walls is placed for the wall to be considered as coupled, is simply the sum of bending moments at the two ends of all coupling beams, transferred from the face of the individual walls to their axes.) No special rules are given for the individual walls, though. Despite their action as a system, these walls are dimensioned in bending and shear as if they were separate. However, the values of the bending moment and the axial force for which the vertical reinforcement is dimensioned do of course reflect the coupling, at least as far as this is captured by the elastic...

## Accidental eccentricity

When the distributions of stiffness and or mass in plan are unsymmetric, the response to the horizontal components of the seismic action has certain torsional-translational features. These features are sufficiently taken into account in an analysis in 3D for the horizontal components, especially when a modal response spectrum analysis or a non-linear dynamic one is performed. Unlike some other seismic design codes, amplification or de-amplification of the 'natural' eccentricities between the centres of mass and stiffness is not required. This is convenient, because normally the storey stiffness centre cannot be uniquely defined (see Section 4.3.2.1). Moreover, determination of the position of a conventionally defined

## Minimum clamping reinforcement across construction joints in walls of DCH

Where NEi is the minimum axial force from the analysis in the seismic design situation (positive when compressive). Equation (D5.50) is derived from the requirement that the combination of cohesion, friction and dowel action at such a joint is not less than the shear stress that may cause shear cracking at a cross-section nearby. According to Eurocode 2, cohesion and friction provide at a naturally rough, untreated interface between concretes cast at different times a design shear resistance equal to

## Design arid detailing roles for timber buildings

This chapter covers the rules for the seismic design of timber buildings, following in a loose Clause 8.1 5 and 6 of EN 1995-1-1. Naturally, in the seismic design situation, the strength modification This is an important departure from analogous recommendations in other sections of EN 1998-1 for other structural materials (namely Section 5 for reinforced concrete, Section 6 for steel and Section 7 for composites), in which it is recommended that 7M values for the fundamental load combinations are used in the seismic design situation. This rule has an important influence on the outcome of the design for the two types of structure (low dissipative and dissipative), and reflects the more reliable response of timber connections and timber structures satisfying the additional requirements for dissipative structures which are set forth in this section of EN 1998-1.

## Invertedpendulum systems

An inverted pendulum is defined as a system with at least 50 of the total mass in the upper third of the height, or with energy dissipation at the base of a single element. Literally, one-storey concrete buildings normally fall in that category. Nonetheless, one-storey frames with the tops of columns connected (through beams) in the two main directions of the building in plan are explicitly excluded from the category, provided that in the seismic design situation the maximum value of the normalized axial load v6 in any column does not exceed 0.3. Such a low value of the axial load, which corresponds to 0.2 for the usual value of 1.5 for the partial factor 7C of concrete, enhances the local ductility at the base of the column. Two-storey frames will not be classified as inverted-pendulum systems, if they have the same mass at the two floors, but will be classified as such if the mass lumped at the roof noticeably exceeds that of the first floor.

## Special requirements for the design of secondary seismic elements

Secondary seismic elements do not need to conform to the rules and requirements given in Sections 5-9 of EN 1998-1 for the design and detailing of structural elements for earthquake resistance based on energy dissipation and ductility they only need to satisfy the rules of the other Eurocodes (2 to 6), plus the special requirement of Eurocode 8 that they maintain support of gravity loads when subjected to the most adverse displacements and deformations induced in them in the seismic design situation. These deformations are determined according to the equal displacement rule, i.e. they may be taken as equal to those computed from the elastic analysis for the design seismic action (neglecting, of course, the contribution of secondary seismic elements to lateral stiffness) multiplied by the behaviour factor, q. They should account for second-order (P-A) effects, by dividing the first-order values by (1 - 6) if the value of the sensitivity ratio Q (see equation (D4.20)) exceeds 0.1....

## Large lightly reinforced walls

Walls with a large horizontal dimension compared with their height cannot be designed effectively for energy dissipation through plastic hinging at the base, as they cannot be easily fixed there against rotation relative to the rest of the structural system. Design of such a wall for plastic hinging at the base is even more difficult if the wall is monolithically connected with one or more transverse walls also large enough not to be considered merely as flange(s) or rib(s) of the first wall. Section 5 recognizes that such walls, due to their large dimensions, will most likely develop limited cracking and inelastic behaviour in the seismic design situation. Cracking is expected to be mainly horizontal and to coincide with construction joints at floor levels. Flexural yielding, if it occurs, will also take place mainly at these locations. Then, the lateral deflections of large walls, acting as vertical cantilevers, will be produced through a combination of (1) a rotation of the...

## Verification for the nolocalcollapse requirement

What was said in Section 2.2.2.1 concerning seismic design for energy dissipation (normally through ductility) with a q factor greater than 1.5, and in Section 2.2.2.2 on design without energy dissipation or ductility and with a q factor not greater than 1.5 for overstrength, applies to buildings. The specific rules for the fulfilment of the no-(local)-collapse requirement within the framework of design for energy dissipation and ductility are elaborated further here. In the standard case of force-based seismic design based on linear analysis with a q factor value greater than 1.5, the following verifications are performed 9 Dissipative zones are dimensioned so that the design resistance of the ductile mechanism(s) of force transfer, Rd, and the design value of the corresponding action effect due to the seismic design situation, Ed, from the analysis satisfy equation (D2.3). Regions of the structure outside the dissipative zones and non-ductile mechanisms of force transfer within or...

## Introduction the level of discretization

According to Section 4 of EN 1998-1, the model of the building structure for linear elastic Clause 4.3.2(1) analysis should represent well the distribution of stiffness in structural elements and of the mass throughout the building. This may not be enough for the purposes of design. As emphasized in the above, the idealization and discretization of the structure should correspond closely to its geometric configuration in 3D, so that it is fit for the main purpose of the analysis, i.e. to provide the seismic action effects for the dimensioning and detailing of members and sections. This means, for instance, that a stick-type model, with all members of a storey combined into a single mathematical element connecting adjacent floors and only three degrees of freedom per storey (for analysis in 3D) is not sufficient for the purposes of seismic design. At the other extreme, a very detailed finite-element discretization, providing very 'accurate' predictions of elastic displacements and...

## Abstract Of The Dissertation

Performance-based seismic design enables the structural engineer to quantify the probability that a building design will satisfy specified seismic performance objectives. A probabilistic assessment of seismic building performance requires the quantification of all of the uncertainties associated with the building design. The research in this dissertation focuses on quantifying the uncertainty in the nonlinear static analysis method to predict building demands. The nonlinear static analysis method was investigated using three different methods for calculating the target roof displacement (1) Coefficient Method, (2) Capacity Spectrum Method, and (3) Equivalent System Method. These methods were used to predict seismic demands on 3-, 9-, and 20-story Pre-Northridge welded steel moment frame buildings using sixty earthquake ground motion records, corresponding to 50 , 10 , and 2 in 50 years seismic hazard levels. The uncertainty in the nonlinear static analysis method was investigated for...

## Compliance criteria for the nolocalcollapse requirement

Cause structures to collapse under their own weight. Force-based seismic design is well established, because structural engineers are familiar with force-based design for other types Fulfilment of the no-(local-)collapse requirement under the design seismic action does not mean that the structure has to remain elastic under this action this would require it to be designed for lateral forces of the order of 50 or more of its weight. Although technically feasible, designing a structure to respond elastically to its design seismic action is economically prohibitive. It is also unnecessary, as an earthquake is a dynamic action, representing for a structure a certain total energy input and a demand to tolerate certain displacements and deformations, but not a demand to withstand specific forces. So, Eurocode 8 allows a structure to develop significant inelastic deformations under its design seismic action, provided that the integrity of individual members and of the structure as a whole is...

## Quantifying Analysis Method Uncertainty Sac Method

The SAC Joint Venture1 research program is currently in the process of finalizing a series of seismic design guidelines (FEMA, 2000) which incorporates the Cornell Demand and Capacity Factor Design (DCFD) methodology for the seismic performance evaluation of steel frame buildings. When an approximate analysis method is used to conduct a seismic performance evaluation of a building, the reliability framework must account for the uncertainty in the analysis method. This section describes the method for quantifying analysis method uncertainty developed as part of the research for the SAC Joint Venture research program and is therefore called the SAC Method. 1 SAC is a joint venture of the Structural Engineers Association of California (SEAOC), the Applied Technology Council (ATC), and California Universities for Research in Earthquake Engineering (CUREe).

## Huntsville Alabama Base Shear Calculations

The Seismic Design Category is determined using the six steps outlined in the code requirements section. First, the site class was determined to be Site Class E for reasons discussed in the preceeding paragraph. Second, the Ground Motion Accelerations were determined from the coefficient maps. The project location fell between contour lines and the value of the higher contour was used as the Code allows. The values are as follows Ss 0.30 and 5, 0.13. Third, the Site Coefficients were Fifth, the Seismic Use Group was determined to be Seismic Use Group I. This facility is not considered an essential facility, it does not provide emergency services or post-earthquake relief functions. It does not have a total occupancy load greater than 5,000 nor does it have conference rooms or auditoriums where large numbers of people congregate. Since it does not fall into Seismic Use Groups II or III, it is classified Seismic Use Group I. Sixth, the Seismic Design Category is determined as a function...

## Secretary to the Task Group B Chan BScHons AMIMechE

Published by The Institution of Structural Engineers 11 Upper Belgrave Street, London SW1X 8BH, United Kingdom Telephone +44(0)20 7235 4535 Fax +44(0)20 7235 4294 Email mail istructe.org.uk Website www.istructe.org.uk 2006 The Institution of Structural Engineers The Institution of Structural Engineers and the members who served on the Task Group which produced this report have endeavoured to ensure the accuracy of its contents. However, the guidance and recommendations given should always be reviewed by those using the report in the light of the facts of their particular case and any specialist advice. No liability for negligence or otherwise in relation to this report and its contents is accepted by the Institution, the members of the Task Group, its servants or agents. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means without prior permission of the Institution of Structural Engineers, who may be contacted at 11...

## S Steel Moment Frame Buildings

To ensure that the beams will yield first, the columns and beam-to-column connections are designed to develop the full strength of the beams. After the 1994 Northridge Earthquake, it was discovered that many of the buildings in the Los Angeles metropolitan area suffered severe damage to their welded beam-column moment connections. Therefore, the beams were not able to yield as intended and dissipate energy through inelastic deformations. The significance of this discovery is that the connection fractures occurred in buildings that otherwise, showed no signs of distress. This discovery sparked the organization of the SAC Joint Venture, a partnership between SEAOC, ATC, and the California Universities for Research in Earthquake Engineering (CUREe). The purpose of the SAC Joint Venture is to investigate the causes of these premature connection fractures, to develop methods to predict the probable earthquake performance, and to develop methods to design and construct more reliable steel...

## Design and detailing of secondary seismic elements

(1)P Clause 5.7 applies to elements designated as secondary seismic elements, which are subjected to significant deformations in the seismic design situation (e.g. slab ribs are not subject to the requirements of 5.7). Such elements shall be designed and detailed to maintain their capacity to support the gravity loads present in the seismic design situation, when subjected to the maximum deformations under the seismic design situation. (2)P Maximum deformations due to the seismic design situation shall be calculated in accordance with 4.3.4 and shall account for P-A effects in accordance with 4.4.2.2(2) and (3). They shall be calculated from an analysis of the structure in the seismic design situation, in which the contribution of secondary seismic elements to lateral stiffness is neglected and primary seismic elements are modelled with their cracked flexural and shear stiffness.

## Evaluation of precast structures

- connections located within critical regions but adequately over-designed with respect to the rest of the structure, so that in the seismic design situation they remain (1) In precast elements and their connections, the possibility of response degradation due to cyclic post-yield deformations should be taken into account. Normally such response degradation is covered by the material partial factors on steel and concrete (see 5.2.4(1)P and 5.2.4(2)). If it is not, the design resistance of precast connections under monotonic loading should be appropriately reduced for the verifications in the seismic design situation.

## Organization of Dissertation

The motivations and objectives for the research in this report are described in Chapter 1. A detailed description of the performance-based design methodology is presented in Chapter 2. A review of state-of-the-art code provisions and recommended guidelines for the design of new buildings and rehabilitation of existing building is presented. A review of nonlinear static pushover analysis methods used to quantify the demands on buildings subjected to earthquake ground motions is presented in Chapter 3. The results of a comparison between the response of the model buildings calculated using the nonlinear static analysis methods and the nonlinear time history analysis method are presented in Chapter 4. Chapter 5 introduces the foundations of reliability-based seismic design. In particular, this chapter describes a reliability-based seismic performance evaluation method called the Cornell Demand and Capacity Factor Design method. Chapter 6 describes the extension of the Cornell method that...

## Estimating Building Response Using Nonlinear Static Analysis Methods

The design of buildings is fundamentally concerned with ensuring that the components of the building, e.g. lateral force resisting system, can adequately serve their intended function. In the case of seismic design of the lateral force resisting system, the design problem can be reduced simply to the problem of providing adequate force and deformation capacity to resist the seismic demands. However, due to the uncertainties associated with the structural materials, the demand and capacity modeling techniques, the methods of analysis used to predict demands, and the prediction of the earthquake ground motions, the seismic demands and structural capacities are not known with certainty. The uncertainties associated with the seismic building demands and structural capacities make it difficult to accurately predict the reliability of the final building design to meet the intended performance objectives. Krawinkler (1997) addressed the importance of quantifying uncertainties in demand...

## Case Study Discussion

The same general outline is used during the project discussion section of this thesis. The project discussion begins with a brief description of the project. Second, the project discussion focuses on the site conditions and results of the geotechnical report. Third, the project discussion walks through the steps of determining the Seismic Design Category as delineated in the code requirements section. Fourth, the discussion moves to seismic base shear, V, calculations and the lateral force at each story by two methods the Simplified Analysis procedure and the Equivalent Lateral Force procedure or the Equivalent Lateral Force procedure and the Modal Response Spectra Analysis procedure. Steps three and four will be repeated for each of the three geographical locations chosen for this study (Huntsville, Alabama Los Angeles, California and Chicago, Illinois). Huntsville, Alabama has medium seismic accelerations Los Angeles, California has high seismic accelerations and Chicago, Illinois...

## International Building Code Seismic Analysis Requirements

The purpose of this section is to provide a basic understanding of the general design considerations and requirements that the International Building Code outlines for seismic design. Section 2.1 reviews overarching design process and takes the reader to the point of determining the method of analysis to be undertaken. The methods of analysis are covered in Sections 2.2 to 2.5.

## S Accounting for secondorder PA effects

Nm is the total gravity load at and above storey i in the seismic design situation, i.e. as determined according to Section 4.4.2. If the vertical members connect floors considered as rigid diaphragms, P-A effects can be accounted for sufficiently according to the previous paragraph. If there are no such floors, or if floors cannot be taken as rigid diaphragms, then P-A effects may be considered on an individual column basis, by subtracting from the column elastic stiffness matrix its linearized geometric stiffness matrix. If the analysis is elastic on the basis of the design response spectrum, the linearized geometric stiffness matrix of each column should be multiplied by the behaviour factor q, to account for the fact that P-A effects should be computed for the full inelastic deformations of the structure and not for the elastic ones which incorporate division by the behaviour factor q. Within the framework of elastic analysis, column axial forces in the geometric stiffness matrix...

## The development of Eurocode

The postwar boom in the construction industry led to a widespread rethinking of the whole civil engineering design process. In the early 1950s, for example, the Institution of Structural Engineers (1955) in the UK set up a committee to report on safety in structural design. In their report, the committee noted that 'the main body of evidence regarding the safety of a structure will usually take the form of design calculations', and they proposed that two particular ratios should dominate the design calculations

## Resistance of foundations

(2)P The action effects for the foundation elements shall be derived on the basis of capacity design considerations accounting for the development of possible overstrength, but they need not exceed the action effects corresponding to the response of the structure under the seismic design situation inherent to the assumption of an elastic behaviour (q 1,0). EF,G is the action effect due to the non-seismic actions included in the combination of actions for the seismic design situation (see EN 1990 2002, 6.4.3.4) Edi is the design value of the action effect on the zone or element i in the seismic design situation. (5) For foundations of structural walls or of columns of moment-resisting frames, Q is the minimum value of the ratio MRd MEd in the two orthogonal principal directions at the lowest cross-section where a plastic hinge can form in the vertical element, in the seismic design situation.

## Analysis Method Uncertainty

The Demand and Capacity Factor Design (DCFD) methodology provides a foundation for reliability-based seismic design and performance evaluation of new and existing buildings. In Chapter 5, the DCFD method was introduced by only taking into consideration the inherent randomness of the building demands and capacities, and neglecting modeling uncertainty. Recall that inherent randomness is uncertainty that is part of nature and is always present, while modeling uncertainty results from the use of approximate models and methods to estimate the building demands and capacities. The fundamental difference in these uncertainties is related to control and reducibility. Unlike inherent randomness, modeling uncertainty can be reduced by using more sophisticated analytical models and methods to calculate the building demands and capacities. In order to provide realistic estimates of building performance, the reliability-based seismic design and performance evaluation methodology must account for...

## Nonlinear timehistory analysis

(2) The structural element models should conform to 4.3.3.4.1(2)-(4) and be supplemented with rules describing the element behaviour under post-elastic unloading-reloading cycles. These rules should realistically reflect the energy dissipation in the element over the range of displacement amplitudes expected in the seismic design situation.

## Summary of key points

The Eurocodes - and in particular, EN 1990 - provide a comprehensive and cohesive framework for ensuring the safety of structures. The engineering concepts that are embodied in them have been used in engineering practice for decades and will be familiar to most structural engineers.

## Tiebeams and foundation beams

(2) Axial forces in tie-beams or tie-zones of foundation slabs in accordance with 5.4.1.2(6) and (7) of EN 1998-5, should be taken in the verification to act together with the action effects derived in accordance with 4.4.2.6(2)P or 4.4.2.6(3) for the seismic design situation, taking into account second-order effects.

## Safety verifications

NOTE 2 The National Annex may specify whether the yM values to be used for earthquake resistant design are those for the persistent and transient or for the accidental design situations. Intermediate values may even be chosen in the National Annex, depending on how the material properties under earthquake loading are evaluated. The recommended choice is that of (2) in this subclause, which allows the same value of the design resistance to be used for the persistent and transient design situations (e.g. gravity loads with wind) and for the seismic design situation.

## Precast largepanel walls

B) in horizontal connections which are partly in compression and partly in tension (under the seismic design situation) the shear resistance verification (see 5.11.2.2) should be made only along the part under compression. In such a case, the value of the axial force NEd should be replaced by the value of the total compressive force Fc acting on the compression area.

## NRdMEd VEd NEdG yov EdE

NEd,G is the compression force in the column or diagonal member due to the non-seismic actions included in the combination of actions for the seismic design situation VEd i, MEd i are the design values of the shear force and of the bending moment in link i in the seismic design situation

## Figure Design envelope of the shear forces in the walls of a dual system Special provisions for large lightly

(4) Unless the results of a more precise calculation are available, the dynamic component of the wall axial force in (3)P of this subclause may be taken as being 50 of the axial force in the wall due to the gravity loads present in the seismic design situation. This force should be taken to have a plus or a minus sign, whichever is most unfavourable.

## Control of differential seismic ground motions

B) The devices constituting the isolation system are fixed at both ends to the rigid diaphragms defined above, either directly or, if not practicable, by means of vertical elements, the relative horizontal displacement of which in the seismic design situation should be lower than 1 20 of the relative displacement of the isolation system.

## Special rules for large wails in structural systems of large lightly reinforced walls Introduction

Eurocode 8 is unique among all regional (as opposed to national) seismic design codes in that it includes special design provisions for structural systems consisting of large walls that cannot be meaningfully designed and detailed for ductile response based on development of a single flexural hinge at the base. Because of this peculiarity, the special dimensioning and detailing provisions given in Section 5 for the large walls of such systems are described in more detail. They are based on the experience of the application of similar rules in the seismic region of the south of France. They apply only to walls that qualify as large and belong in a structural system of large lightly reinforced walls.

## Design Of Buildings

(1)P A certain number of structural members (e.g. beams and or columns) may be designated as secondary seismic members (or elements), not forming part of the seismic action resisting system of the building. The strength and stiffness of these elements against seismic actions shall be neglected. They do not need to conform to the requirements of Sections 5 to 9. Nonetheless these members and their connections shall be designed and detailed to maintain support of gravity loading when subjected to the displacements caused by the most unfavourable seismic design condition. Due allowance of 2nd order effects (P-A effects) should be made in the design of these members. (1)P For the purpose of seismic design, building structures are categorised into being regular or non-regular. (2) This distinction has implications for the following aspects of the seismic design

## General

Part 1.1 of Eurocodc 3 is the basic document on which this text concentrates, but designers will need to consult other sub-parts, for example Part 1.8, for information on bolts and welds, and Pari Lit), for guidance on material selection, since no duplication of content is permitted between codes. It is for this reason that it seems likely that designers in the UK will turn first to simplified and more restricted design rules, for example SCI guides and manuals produced by the Institutions of Civil and Structural Engineers, whilst referring to the Eurocode documents themselves when further information is required. Given that some reference to the content of EN 1990 on load combinations and to EN 1991 on loading will also be necessary when conducting design calculations, working directly from the Eurocodes for even the simplest of steel structures requires the simultaneous use of several lengthy documents.

## Background

Formal consideration of the permanent seismic wall displacement in the seismic design process for Corps-type retaining structures is given in Ebeling and Morrison (1992). The key aspect of this engineering approach is that simplified procedures for computing the seismically induced earth loads on retaining structures are dependent upon the amount of permanent wall displacement that is expected to occur for each specified design earthquake. The Corps uses two design earthquakes as stipulated in Engineer Regulation (ER) 1110-2-1806 (Headquarters, U.S. Army Corps of Engineers (HQUSACE) 1995) the Operational Basis Earthquake (OBE)1 and the Maximum Design Earthquake (MDE). The retaining wall would be analyzed for each design case. The load factors used in the design of reinforced concrete hydraulic structures are different for each of these two load cases. Rotational response of the wall (compared to sliding) is beyond the scope of the Ebeling and Morrison (1992) simplified engineering...

## Appendices

It does not cover seismic design, which is the subject of Eurocode 8 and in 9.1(1) it is stated implicitly that dykes and dams are also excluded. EC1,1.1 states that it does not completely cover structures which require unusual reliability considerations, such as nuclear structures. By implication, this applies to the full suite of Eurocodes.

## Research Motivation

Starting in the early 1990's, the direction of building design in seismic regions has been towards Performance-Based Seismic Design. The objective of this building design method is to accurately predict, in definable terms, the performance of a building during any intensity of earthquake ground motion that may occur at the building site during the design life of the building. Definable building performance can be accomplished by designing the building to meet a range of performance objectives. A single performance objective consists of a clear definition of a level of building performance, quantified in terms of damage, and a level of earthquake hazard. For example, a building may be designed to be at the brink of collapse during an earthquake that is expected to occur once every 2,500 years. Predictable building performance can be established if the engineer can quantify the reliability of the final design to meet the stated performance objectives. previously discussed, a...

## Beams and columns

Resistance with the bending moment MEd, defined as its design value in the seismic design situation NEd,G is the axial force in the beam or in the column due to the non-seismic actions included in the combination of actions for the seismic design situation NEd i is the design value of the axial force in the same diagonal i in the seismic design situation.

## Vision2000 Oes1995

The DCFD methodology developed by Jalayer and Cornell can be used to directly satisfy the design verification steps of the performance-based seismic design methodology introduced by Vision 2000 (OES, 1995). Prior to design verification, the building owner selects the performance objectives for the building. Each performance objective consists of a level of earthquake ground motion associated with a performance level, e.g. 2 in 50 year ground motion and the Near Collapse performance level. Each performance level has an associated description of structural, architectural and content damage, and acceptable values of building response quantities. For example, Table 2.1 in Chapter 2 shows the Vision 2000 definition of the Near Collapse performance level. For

## Safety verification

(3) In ultimate limit state verifications for the seismic design situation, partial factors ym for masonry properties and ys for reinforcing steel should be used. NOTE The values ascribed to the material partial factors ym and ys for use in a country in the seismic design situation may be found in its National Annex of this document. The recommended value for ym is 2 3 of the value specified in the National Annex to EN 1996-11 2004, but not less than 1,5. The recommended value for ys is 1,0.

## Conclusions

Soil properties would be more favorable to most designs if all soil strata in the top 100 feet were used in the seismic design soil properties. procedure, if a more rigorous Modal Response Spectra analysis is undertaken. Additionally, further research would need to be undertaken to quantify the impact of considering all soil strata in the top 100 feet in the seismic design soil properties.

## Info

The SAC Joint Venture research program is currently in the process of finalizing a series of seismic design guidelines (FEMA, 2000) which incorporates the Cornell DCFD methodology for the seismic performance evaluation of steel frame buildings. Appendix D describes the method used to quantify analysis method uncertainty for the SAC research program. In addition, the following sections describe two alternate methods for quantifying analysis method uncertainty. Section 6.3.1 provides recommended values of the first- and second-order statistics of the bias factors that are dependent of the level of seismic hazard based on the results presented in Chapter 4. Section 6.3.2 describes a method for incorporating analysis method uncertainty in the DCFD methodology that does not depend on the level of seismic hazard.

## National foreword

ENV 1997-3 1999 results from a programme of work sponsored by the European Commission to make available a common set of rules for the structural and geotechnical design of buildings and civil engineering works. The full range of codes covers the basis of design and actions, the design of structures in concrete, steel, composite construction, timber, masonry and aluminium alloy, and geotechnical and seismic design.

## Resistance condition

Ed is the design value of the action effect, due to the seismic design situation (see EN 1990 2002 6.4.3.4), including, if necessary, second order effects (see (2) of this subclause). Redistribution of bending moments in accordance with EN 1992-1-1 2004, EN 1993-1 2004 and EN 1994-1-1 2004 is permitted Ptot is the total gravity load at and above the storey considered in the seismic design situation (6) Fatigue resistance does not need to be verified under the seismic design situation.

## Mkbmin

(XMRd c)i is opposite (the same at end ). Factor 7Rd accounts again for possible overstrength due to steel strain hardening, and is taken equal to 7Rd 1 for beams of DCM and to 7Rd 1.2 for beams of DCH. ld is the clear length of the beam between the end sections, and Vg+4a n(x) is the shear force at cross-section x due to the vertical loads in the seismic design situation, g + ipjCj, with the beam considered as simply supported (index o). Vg+il2q0(x) may be conveniently computed (especially if the loads g + ip2q are not uniformly distributed along the length of the beam) from the results of the analysis of the structure for the vertical loads, r + i )2q, alone, as the shear force V +,i 2q_ 0(x) at cross-section x in the full structure, corrected