Behaviour factors of structural types similar to steel

Clauses 7.3.1, The values of q factors for composite structures are the same as in steel structures with 7.3.2 the same structural system, namely moment-resisting frames,84 or frames with concentric or eccentric bracings, as given in Table 6.2 in EN 1998-1. There are, however, some limitations for these types of composite structures, which deserve an explanation. These limitations are Braces of composite concentrically braced frames cannot be composite (clause 7.3.1(l)b). Clause 7.3.1(1)...

Bidirectional resistance and stiffness

Seismic motion is a multi-directional phenomenon. In particular, its bi-directionality in the horizontal plan has to be considered in the conceptual design of the structure of a building. Accordingly, it is not surprising that Eurocode 8 requires that a building must be able to resist horizontal actions in any direction. A very straightforward - and indeed the most common - way to achieve this is to arrange the structural elements in an orthogonal in-plan structural pattern. It is furthermore...

Conception of structures for earthquake resistant buildings

It is well known that a good seismic response of a building is much more easily achievable if Clause 4.2.1(1) its structural system possesses some characteristics that enable a clear and simple structural response under the action of the seismic event. Such characteristics, being basic features of any structural system developed for a building, have to be considered and incorporated at the very earliest phases of the structural design i.e. at the conceptual design phase, which is the root of...

Control of design and construction

The requirement on control of design and construction of steel buildings in EN 1998-1 Clause 6.11 reflects the concern expressed in Section 6.3 about creating the conditions for an effective global dissipative behaviour of the structure. This goal requires in particular that the yield stress of all materials used in the dissipative components remains within well-defined ranges, notably below an upper bound value. The complete background of these requirements has Regarding problems with...

Design against localization of strains

Clauses 6.5.5(I), In Eurocode 8, design against localization of strains is stated as a general requirement for 6.5.4(1), 7.5.4(1) joints in clause 6.5.5(1). No imposed design of connections is provided. Some explicit rules are related to the mitigation of strain localization. Conformity to standards on steel material is one of them The development of a dissipative zone involves a 'spreading' of yield, which requires strain hardening. As the material becomes harder with plastic strains,...

Dissipative versus lowdissipative structures

Steel buildings can be designed to be 'energy-dissipative' to a larger or smaller extent. As Clauses 6.1.2(1), also explained in Section 2.2.2.1 of this guide, this term refers to the ability of some 6.1.2(2), intentionally selected parts of the structure to safely undergo cyclic plastic deformations, and 6.1.2(4), applies to buildings designed such that the selected zones - and only those - are indeed 6.1.2(5), activated plastically. Then, the global behaviour of the building under seismic...

Effective width of slabs

Tables 7.5.1 and 7.5.II EN 1998-1 for the effective width b,, of the slab in composite beams have been established for moment-resisting frames with rigid connections in which The local plastic mechanism in dissipative zones is such that the integrity of the concrete slab is maintained during the seismic event. In fact, the values provided for be achieve that goal in the first stage of plastic rotations, but, as the rotations increase, some degradation of concrete adjacent to the column may...

Exemption from the application of Eurocode

Clauses 2.2.1 (4), Eurocode 8 itself states that its provisions need not be applied in cases of very low seismicity. 3.2.1 (5) As for cases of low seismicity, which combination of categories of structures, ground types and seismic zones in a country will qualify as cases of very low seismicity is left to the National Annex. However, it recommends (in a note) the same criterion as for the cases of low seismicity either the value of the design ground acceleration on type A ground (i.e. on rock),...

Modelling of beams columns and bracings

Beams, columns and bracings are normally modelled as prismatic 3D beam elements, characterized by their cross-sectional area, moments of inertia, Iy and I7, with respect to the principal axesy andz of the cross-section, shear areas andAz along these local axes (for shear flexibility, which is important in members with low length-to-cross-sectional-depth ratio) and torsional moment of inertia, C or Ix for St Venant torsion about the member centroidal axis x. Members with a cross-section...

S Introductory remark

Section 7 on composite buildings in EN 1998-1 has a similar structure to Section 6 on steel Clauses 7.1.2(5), buildings. The information provided for steel buildings in Section 6 applies to composite 7.1.2(6), buildings as well. In the following, the emphasis is placed on those aspects which are specific 7.7.5(1), to the composite character of structural elements and structural types. 7.7.5(2) The section on composite buildings in Eurocode 8 has been developed on the basis of one general design...

Selection of the behaviour factor for design purposes

The values of behaviour factors q provided in Table 6.2 of EN 1998-1 are the maximum Clause 6.3.2(1) allowed values. The designer can always decide to work with a smaller q. This can be justified in some cases by the fact that, as mentioned in Section 6.2, the seismic design condition is not necessarily the most controlling factor for the structure, and trying to make use of the highest possible value of q may have no practical impact. It should be stressed that, whatever the value of q used in...

Selection of the typology of eccentric bracings

There are many possible typologies of eccentric bracings, involving seismic links, which can be either short or long. The choice between short and long links is partly determined by the following considerations Short links provide more stiffness than long ones. Shear deformations essentially are in-plane deformations of the web of the link section, without a marked tendency to lateral torsional buckling. Long links mean strong bending effects and plastic hinges in bending with buckling of...

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...

The inadequacy of member models in D as a limitation of nonlinear modelling

It is natural to expect that a sophisticated method (in this case non-linear seismic response analysis) will be at least as good at tackling general design situations in their full complexity as simplified approaches (in the present case, linear seismic response analysis). However, as already noted, the non-linear static (pushover) analysis method has been developed for analysis of seismic response in 2D (regardless of whether a 3D structural model is used), and its application in cases of...

Estimation of the effects of accidental eccentricity through static analysis

Even when the modal response spectrum method is used for the analysis of the response to Clause the two horizontal components of the seismic action, Eurocode 8 allows a static analysis for 4.3.3.3.3(I) the effects of the accidental eccentricities of these components. In this analysis, a 3D structural model is subjected to storey torques about the vertical axis, which have all the same sign and are equivalent to the storey lateral loads due to the horizontal component considered multiplied by...

S Accounting for secondorder PA effects

Section 4 of EN 1998-1 requires taking into account second-order (P-A) effects in buildings, when for the vertical members of the storey, these exceed 10 of the first-order effects in the aggregate. The criterion is the value of the interstorey drift sensitivity coefficient, 9, defined for storey i as the ratio of the total second-order moment in storey i to the change in the first-order overturning moment in that storey Nm is the total gravity load at and above storey i in the seismic design...

Compliance criteria for the nolocalcollapse requirement

Norway Seismic Spectrum

The no-(local-)collapse performance level is considered as the ultimate limit state against Clauses 2.2.1(1), which the structure should be designed according to the EN 1990 on the basis of structural 2.2.2(I), design.3 Unlike the damage limitation limit state, which is verified on the basis of deformation- 2.2.2(2) based criteria, design for the no-(local-)collapse ultimate limit state is force-based. This is against the physical reality showing that it is the deformation that causes a...

Compliance criteria for damage limitation

An earthquake represents for the structure a demand to accommodate a given energy input Clauses 2.2.1 1 , or given imposed dynamic displacements. Seismic damage to structural elements, or even to 2.2.3 I non-structural ones that follow the deformations of the structure, is due to deformations induced by the seismic response. Consistent with this reality, Eurocode 8 states that compliance criteria for the damage limitation limit state i.e. performance level should be expressed in terms of...

MviAxi max xi

Is used in the dimensioning of the shear reinforcement of DCH beams as a measure of the reversal of the shear force at end i similarly at end ' . The design shear force in primary seismic columns and beams of buildings of DCM or DCH is always computed through equations D5.12 and D5.13 , without exemptions. In beams and columns with short clear length ld, these expressions give a large value of the design shear force. Short columns are very vulnerable to the high shear force resulting from...

Scope of Eurocode Part I

Although its main object is buildings, EN 1998-1 also includes the general provisions for the EN 1998-1 other parts of Eurocode 8 to build on clause 1.1.2 analysis procedures and general concepts and rules applicable to all structures beyond buildings. Table I.I. Eurocode 8 parts and key dates achievement or expectation, as of January 2005 Availability from CEN of approved EN in English, French, and Availability from CEN of approved EN in English, French, and Table 1.2. Eurocode 8 parts in...

Introduction the level of discretization

In constructing the structural model of a building for the purposes of its earthquake-resistant design, the designer should keep in mind that his or her objective is the design of an earthquake-resistant structure and not the analysis perse. This ultimate objective is pursued through a long process, an intermediate stage of which is normally a linear elastic analysis of a mathematical model of the structure, as conceived. A subsequent, and at least equally important phase, is that of the...

Simplified design of frames with decoupled diagonal bracings

The structural behaviour of decoupled diagonal bracings is similar to that of X bracings, but as there are two braced zones, each containing one diagonal instead of two, the problem of overstrength described above for X bracings takes place differently, as twice as many columns are involved in the bracing. For this reason, clause 6.7.3 2 states that no lower bound value of slenderness restricts the possible dimensions of the diagonals in this case. However, to be complete the design must also...

Systems of large lightly reinforced walls

Eurocode 8 is unique among international codes in that it includes special provisions for systems consisting of a fairly large number of large but lightly reinforced concrete walls which are designed to sustain seismic demands not by dissipating kinetic energy through hysteresis in plastic hinges but by converting part of this energy into potential energy of the masses and returning part to the ground through radiation from their foundation. To qualify for the special design provisions of...

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. 4.11.2.1. Verification in...

Nondissipative composite columns

The majority of column members are non-dissipative, because the intended global dissipative mechanisms of structures involve as little energy dissipation in columns as possible. For this reason, only their elastic response needs to be assured, which is done essentially by complying to Eurocode 4. There are, however, differences between a standard design to Eurocode 4 and the earthquake context. The origin of the first difference is in the 'cyclic' aspect of the response, which can degrade the...

Analysis of frames with concentric bracings considering their evolutive behaviour

Clauses 6.7.1 1 , In Eurocode 8, the design concept for frames with concentric bracings is that diagonals in 6.7.2 2 tension are the reliable dissipative zones, while diagonals in compression buckle and do not contribute significantly to stiffness and resistance. The problem is that the reality is evolutive. In a first stage, the compression action effect in the diagonal can increase up to the buckling strength ,Npl Rd however, in the following cycles the strength of that diagonal in...

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....

Design of dissipative zones

Clauses 6.6.4 2 , As mentioned before, dissipative zones in moment-resisting frames should be plastic hinges 6.6.4 3 , activated by bending moments. They appear at beam ends, due to the shape of the bending 6.6.4 5 , moment diagram under the seismic action see Fig. 6.8 . 6.6.4 6 , Plastic hinges can take place in the connections, in the case of partial-strength or semi-rigid 6.5.5 7 connection design. There are many possible designs, using connecting components of various types flexible end...

Special modelling considerations for walls

The marked preference of Section 4.6.1 in favour of member-type modelling, representing Clause every individual structural member between connections to others as a single 3D beam 5.4.3.4.1 4 element, applies also to concrete, masonry or even composite steel-concrete walls, or at least to parts of such walls between successive floors and or substantial openings. Such modelling of walls is often called 'wide-column analogy'. Supporting this position is the requirement of Section 5 of EN 1998-1...

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...

Scope of Eurocode

Eurocode 8, Design of Structures for Earthquake Resistance, covers, as its title suggests, the EN 1998-1 earthquake-resistant design and construction of buildings and other civil engineering works clauses 1.1.1 1 , in seismic regions. Its stated purpose is to protect human life and property in the event of I.I.I 2 , earthquakes and to ensure that structures which are important for civil protection remain 1.1.1 4 , Eurocode 8 has six parts, listed in Table 1.1. Among them, only Parts 1 EN...

Regularity in elevation

Criteria for structural regularity in elevation A building is characterized as regular in elevation if it meets all the following conditions Its lateral force-resisting systems moment frames or frames with bracings, walls, etc. should continue from the foundation to the top of the relevant part of the building. 8 The storey mass and stiffness should be constant or decrease gradually and smoothly to the top. 8 In frame buildings, there should be no abrupt variations of the overstrength...

Simplified design of frames with V bracings

The simplified design approach for V or A bracings called inverted V in Eurocode 8 and 'chevron' bracings in North American terminology is different from that considered for X bracings, due to the fact that both the tension and the compression diagonals are considered Clauses 6.7.2 1 , 6.7.4 1 , 6.7.3 1 , 6.7.3 2 , 6.7.3 3 , 6.7.3 4 in the analysis. This results in higher computed stiffness and strength of the structure with respect to an analysis ignoring the compression diagonal. This more...

Uniformity symmetry and redundancy

Uniformity, symmetry and redundancy are related characteristics which are normally correlated to structural simplicity The advantage of structural uniformity in the seismic design context is that it allows the inertial forces created in the distributed masses of the building to be transmitted via short and direct paths, avoiding longer or indirect paths. Structural uniformity of the building should be sought both in plan and in elevation. To achieve plan uniformity and symmetry , it may be...

Verification of beamcolumn joints in shear

Clauses Assuming that bond strength along the beam and column bars framing the joint core is 5.5.3.3 I , sufficient to transfer into the joint the full shear force demand, given by equation D5.20 in 5.5.3.3 2 , terms of the horizontal shear force, Vjhd, the body of the joint then resists that shear. This 5.5.3.3 3 shear force is translated into a shear stress, considered uniform within the joint volume, defined by the horizontal distance between the extreme layers of column reinforcement, h-,...

Boundary elements at section ends in the critical region of ductile walls

As noted in the definition of walls in Section 5.2.2, what mainly differentiates the design and Clauses detailing of a wall as a concrete member from that of a column is that for a wall, flexural 5.4.3.4.2 6 , resistance is assigned to the opposite ends of the section flanges, or tension and compression 5.5.3.4.5 6 chords and shear resistance to the web in between. This is accomplished by concentrating the vertical reinforcement and limiting the confinement of the concrete only at the two ends...

Short links versus long links

Clauses 6.8.2 3 , Seismic links are designed for the computed seismic action effect in shear or in bending of 6.8.2 4 , the link, by complying to 6 8 2 8 ' FEd P,Knk MEd,Mp,link D6.9 6.8.2 9 which Vp_link and Mp Mnk are, respectively, the plastic shear and bending resistance of the K, link fy K d - if Mp gt link fybtl d - Q D6.10 Equation 6.17 in EN 1998-1 allows computation of Vp link taking into account the interaction of shear with axial force, while equation 6.18 in EN 1998-1 allows...

Structural types and behaviour factors

Concrete Frames

Clauses 6.3.1, The behaviour factor q characterizes the ability of a structure to dissipate energy in plastic 6.3.2 I deformations. A structure can provide high values of q if 9 dissipative zones are able to undergo significant plastic deformations without losing strength 9 the topology of the structure is such that a large number of dissipative zones are activated. The values given in Table 6.2 of EN 1998-1 have been determined in background studies however, there is a direct logic relating...

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 way Section 8 of EN 1998-1. However, it does not elaborate on all clauses in that section and neither does it strictly follow the sequence of clauses. It is important to stress that for the overall design of a timber building, the rules of EN 1998-1 are additional to those presented in EN 1995-1-1. 8.2. General concepts in earthquake resistant timber buildings Timber is generally considered...

Minimum clamping reinforcement across construction joints in walls of DCH

An additional requirement for DCH walls is to provide across all construction joints clamping reinforcement at a minimum ratio 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...

Performance requirements for new designs In Eurocode and associated seismic hazard levels

As a European standard EN , Part 1 of Eurocode 8 provides for a two-level seismic design Clause 2.1 1 with the following explicit performance objectives No- local- collapse protection of life under a rare seismic action, through prevention of collapse of the structure or its parts and retention of structural integrity and residual load capacity after the event. This implies that the structure is significantly damaged, and may have moderate permanent drifts, but retains its full vertical...

Detailing of the reinforcement

Reinforced Concrete Rules Splicing

Clauses As stated above, wherever the large wall can resist the design shear force FEd without 5.4.3.5.3 1 , horizontal reinforcement, then it can be constructed without such reinforcement. The 5.4.3.5.3 2 minimum horizontal reinforcement at a recommended amount given in Eurocode 2 for walls subjected to non-seismic actions has to be placed only wherever the wall needs horizontal reinforcement to resist the design shear force. As there is no specific mention of minimum vertical reinforcement in...

S General requirements for nonlinear modelling

Modelling for the purposes of non-linear analysis should be an extension of that used for linear methods, to include the post-elastic behaviour of members beyond their yield strength. Put differently, as a non-linear analysis degenerates into a linear one if member yield strength is not attained during the seismic response, in the linear range of behaviour, modelling for non-linear analysis should be consistent with that used for linear analysis. Consistency does not imply that the level of...

Identification of ground types

Clause 3.1.2 1 The influence of the local soil condition on the seismic response of structures can be quantified by defining ground types with different mechanical properties. Five ground types have been selected to identify the soil profiles. Alphabetical capital letters A, B, C, D and E are used for such profiles. Table 3.1 of EN 1998-1 'ground types1 provides for each ground type a description of the stratigraphic profile and the parameters used to classify the soil. Three parameters have...

Cracked stiffness in concrete and masonry

Clauses 4.3.1 6 , A fundamental assumption underlying the provisions of Eurocode 8 for design for energy 4.3.1 7 dissipation and ductility is that the global inelastic response of a structure to monotonic lateral forces is bilinear, close to elastic-perfectly-plastic. The elastic stiffness used in analysis should correspond to the stiffness of the elastic branch of such a bilinear global force-deformation response. This means that the use of the full elastic stiffness of uncracked concrete or...

Ductile walls coupled and uncoupled

The main type of wall according to Section 5 is the ductile wall, designed and detailed to dissipate energy in a flexural plastic hinge only at the base and to remain elastic throughout the rest of its height, in order to promote - or even force - a beam-sway plastic mechanism for a flexural plastic hinge with high ductility and dissipation capacity to develop at the base, the ductile wall should be fixed there so that relative rotation of its base with respect to the rest of the structural...

Design and detailing of foundation elements

Foundation elements are normally made of concrete, even when the superstructure may consist of another structural material. Section 5 gives the design and detailing rules which apply to concrete foundation elements footings, tie beams, foundation beams, foundation slabs and walls, piles and pile caps even when the vertical elements founded through them are made of a different material. Section 5 also gives rules for the connection of concrete foundation elements to the vertical ones of the...

Dimensioning for the ULS in bending with axial force

Large walls should be dimensioned for the ULS in flexure without any increase of the design Clauses moments above the base over those obtained from the analysis for the seismic design 5.4.3.5.1 1 , situation. Moreover, the vertical reinforcement placed in the cross-section should be tailored 5.4.3.5.3 3 to the requirements of the ULS in flexure with axial force - e.g. without excess reinforcement and with less minimum web vertical reinforcement than required in ductile walls. The objective is...

Maximum longitudinal reinforcement ratio in the critical regions of beams

Clauses In beams the value of specified via equations D5.ll for plastic hinge regions is provided 5.2.3.4 2 , through an upper limit on the ratio of the tension longitudinal reinforcement in the critical 5.2.3.7 3 a , regions, p, max Asl mJbd. The value of pL max is derived as follows. 5.4.3.1.2 3 , When the tension reinforcement is less than that in compression, A,, lt As2, the ultimate 5.4.3.1.2 4 deformation at the end of the beam will take place when the effective ultimate strain of the...

Partial strength connections

Partial Strength Connections

Clause 6.7.3 9 Partial strength connections are not a familiar option in frames with concentric bracings, though several reasons justify the statement that concentric bracings are an excellent application field for such connections. These reasons are 0 Frames with concentric bracings possess a high stiffness because of their topology, and easily fulfil deformation criteria. Thus, unlike moment-resisting frames, additional flexibility in the connections is not penalized by the need to increase...

Design rules aiming at the realization of dissipative zones

Clause 6.2 The following clauses of Eurocode 8 aim at creating conditions for an effective local dissipation of energy based on the principle of capacity design Clause 6.2 defines conditions on material properties such that the yield stress of the different components is under control and the ductile 'weak link' is really a weak link in the chain of resistances. Clause 6.5.5 3 For design in which dissipative zones are intended in the structural elements and not in the connections, a factor of...

Introduction and scope

Field experience and analytical and experimental research have demonstrated the overall Clause 2.2.2 6 beneficial effect of masonry infills attached to the structural frame on the seismic performance of buildings, especially when the building structure has little engineered earthquake resistance. If they are effectively confined by the surrounding frame, infill panels reduce, through their in-plane shear stiffness, storey drift demands, increase, through their in-plane shear strength, the...

Overview of the menu of analysis methods

Section 4 of EN 1998-1 provides the following analysis options for the design of buildings and for the evaluation of their seismic performance linear static analysis termed the 'lateral force' method of analysis in EN 1998-1, but often in practice called 'equivalent static' analysis modal response spectrum analysis also termed in practice 'linear dynamic' analysis, with the risk of being confused with linear time-history analysis non-linear static analysis commonly known as 'pushover' analysis...

S I Frames with eccentric bracings

General features of the design of frames with eccentric bracings The geometry of frames with eccentric bracings is close to that of frames with concentric bracings some intentional eccentricities in the layout of bars generate bending moments and shear. These structures resist horizontal forces essentially by axially loaded members, but they are designed to yield first in shear or bending in 'seismic links'. The latter are zones created by the shift of bars of the reference concentric...

Shear verification in the critical region of ductile walls

Similarly to beams and columns, the design value of the shear resistance of ductile walls, as controlled by the transverse reinforcement, FRd s, or by diagonal compression in the web, KRd max, is computed according to the rules of Eurocode 2 for monotonic loading, except for DCH walls and especially in their critical region. The special rules applicable for DCH walls are detailed below. In the critical region of DCH walls, the design value of the cyclic shear resistance, as controlled by...

Definition and role of primary and secondary seismic elements

Clauses 4.2.2 1 , EN 1998-1 recognizes that a certain number of structural elements which are not essential 4.2.2 3 parts of the seismic-resisting structural system of the building may be considered as'secondary 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...

Torsional resistance and stiffness

Torsional stiffness and resistance are characteristics of building structures which significantly Clause 4.2.1.4 1 influence their response to seismic actions. Responses in which translational motion is dominant are preferable to those in which torsional motion is significant because they tend to stress the different structural elements in a more uniform way. To counteract the torsional response of buildings, the fundamental modes of vibration of the structure should be translational or mainly...

Momentresisting frames

Steel Beam Lateral Buckling

Clause 6.6.1 I Like moment-resisting frames made of other materials, the design objective for steel moment frames is that plastic hinges form in the beams and not in the columns. This requirement is waived at the base of the frame, at the top floor of multi-storey buildings and for one-storey buildings. This requirement is assumed to be fulfilled if equation D4.23 is satisfied. Equation D4.23 expresses a local hierarchy criterion between plastic resistances of beams and columns intersecting at...

Design of beams and columns

Web Panel Zone Shear

In beams of classes 1 and 2, the value of bit of walls of sections are such that local buckling only takes place after substantial plastic rotations, large enough to fulfil the plastic rotation demand from the earthquake. The prevention of lateral torsional buckling is another serious concern in beam elements, in particular those made of H or I sections, due to coupling between the local and lateral buckling instability phenomena inward buckling on one side of the flange is accompanied by...

Nonlinear methods of analysis

Introduction field of application The primary use of non-linear methods of analysis within the framework of Eurocode 8 is to evaluate the seismic performance of new designs, or to assess existing or retrofitted buildings. In fact, in EN 1998-3 on the assessment and retrofitting of buildings the reference analysis methods are the non-linear ones. In the context of EN 1998-1, non-linear methods are limited to the detailed evaluation of the seismic performance of a new building design...

Favourable factors for local ductility

Steel is a ductile material, if a correct steel grade is selected a material elongation over 20 and a material ductility ratio e rnaj ey over 10 can provide highly ductile dissipative zones. If the designer makes good choices in the design, the plastic mechanism developed in a structural component, such as a beam or a diagonal bar in a truss, can be fairly ductile and dissipative. Reliable energy dissipation at the element scale can be found in 1 Bars yielding in tension. This possibility...

Elevation Regularity Eurocode

Clauses There is plenty of evidence from damage observation after earthquakes that regular buildings 4.2.3.1 1 , tend to behave much better than irregular ones. However, a precise definition of what is a 4.2.3.1 2 , regular structure in the context of the seismic response of buildings has eluded many 4.2.3.1 3 attempts to achieve it. There are so many variables and structural characteristics that may or should be considered in such a definition that the classification of a building as 'regular'...

Combination of the effects of the components of the seismic action

The two horizontal components of the seismic action and the vertical one when it is taken into account are considered to act simultaneously on the structure. Simultaneous occurrence of more than one component can be handled only by a time-history analysis of the response which in Eurocode 8 is meant to be non-linear . All other analysis methods give only estimates of the peak values of seismic action effects during the response to a single component. These are denoted here as Ex and EY for the...

Behaviour factor q of concrete buildings designed for energy dissipation

In building structures designed for energy dissipation and ductility, the value of the behaviour Clause 5.2.2.2 factor q, by which the elastic spectrum used in linear analysis is reduced, depends on the type of lateral-force-resisting system and on the ductility class selected for the design. As we will see in Section 5.6.3.2 the value of the q factor is linked, directly or indirectly, to the local ductility demands in members and hence to the corresponding detailing requirements. As in DCL...

Seismic zones

Return Period

This section aims to define the seismic action used to perform structural analysis and to Clauses 3.2.1 1 , design building systems according to the rules specified in the relevant parts of Eurocode 8. 3.2.1 2 Typical representations of seismic actions are described. These include basic spectrum based and alternative accelerograms formats. Also, expressions for combining the seismic action with other actions are given. Seismic zones are introduced along with the engineering seismological...

Basic representation of the seismic action

Nonlinear Damping Characteristics

Clause 3.2.2.1 Methods for evaluating earthquake input for different hazard levels include zonation map-based procedures and site-specific studies. The latter are primarily employed for large projects, such as long bridges, nuclear power plants and or when site amplification effects, e.g. on soft soil sites, are expected. It is also the only approach feasible in the assessment of geographically distributed systems subjected to spatially varying ground motion. Soft soil sites filter out short...

Dimensioning of shear reinforcement in critical regions of beams and columns

Clauses The design value of the shear resistance of beams or columns is computed according to the 5.4.3.1.1 1 , rules of Eurocode 2 for monotonie loading, both when it is controlled by the transverse 5.4.3.2.1 1 , reinforcement, VRd s, and when it is controlled by diagonal compression in the web of the 5.5.3.2.1 1 member, FRd max. There is one exception to this the value of FRd s in the critical regions of beams of DCH. The special rules for FRd s in this particular case are described below....

Maximum diameter of longitudinal beam bars crossing beamcolumn joints

Shear forces are introduced to beam-column joints primarily through bond stresses along Clause 5.6.2.2 2 the beam and column longitudinal bars framing the joint core. Equation D5.21 above giving the design shear force in the joint presumes that bond strength along the beam top bars is sufficient for the transfer of this shear force. Although loss of bond along these bars will not have dramatic global consequences, it would be better avoided through verification of bond along the bars of the...

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...

Dimensioning for the ULS in shear

Strut And Tie Model

To preclude shear failure, each large wall is dimensioned for a shear force, VFd. obtained by multiplying the shear force from the analysis for the design seismic action, VEd, by a magnification factor e For the usual value of q 3 applying to systems of large lightly reinforced walls, the value of e is equal to 2, and exceeds that given by equation D5.19 for ductile walls of the same ductility class M . Moreover, as the rules for dimensioning the vertical reinforcement explicitly request...

The lateral force method of analysis

Introduction the lateral force method versus modal response spectrum 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...

LI Verification for damage limitation

Clauses The damage limitation requirement for buildings is simply an upper limit on the interstorey 4.4.3.1 1 , drift ratio demand under the frequent serviceability seismic action. The limit on the 4.4.3.2 I interstorey drift ratio is set equal to 1 0.5 , if there are brittle non-structural elements attached to the structure so that they are forced to follow structural deformations normally partitions 2 0.75 , if non-structural elements partitions attached to the structure as above are ductile...

Diaphragmatic behaviour at the storey level

In building structures the floors act as horizontal diaphragms that collect and transmit the Clause 4.2.1.5 1 inertia forces to the vertical structural systems and ensure that those systems act together in resisting the horizontal seismic action. The action of these diaphragms is especially relevant to complex and non-uniform layouts of the vertical structural systems because, in these cases, as indicated above, the inertia forces created in the distributed masses of the building have to be...

Special modelling requirements for nonlinear dynamic analysis

Clause In order to be used in non-linear response-history analysis, member force-displacement 4.3.3.4.3 2 models need only be supplemented with hysteresis rules describing the behaviour in post-elastic unloading-reloading cycles. The only requirement posed by Eurocode 8 for the hysteresis rules is to reflect realistically energy dissipation within the range of displacement amplitudes induced in the member by the seismic action used as input to the analysis. Given that the predictions of...

Designers Guide to EN and EN

Eurocode 8 Design of structures for earthquake resistance. General rules, seismic actions, design rules for buildings, foundations and retaining structures Michael N. Fardis, Eduardo Carvaiho, Amr Elnashai, Ezio Faccioli, Paolo Pinto and Andre Plumier DESIGNERS' GUIDE TO EN 1998-1 ND EN 1998-5 EUROCODE 8 DESIGN OF STRUCTURES FOR EARTHQUAKE RESISTANCE GENERAL RULES, SEISMIC ACTIONS, DESIGN RULES FOR BUILDINGS, FOUNDATIONS AND RETAINING STRUCTURES M. FARD IS, E. CARVALHO, A. ELNASHAI, E....

Seismic reinforcement in the concrete slab in momentresisting frames

Steel Frame Detailing

Under the design seismic action, the bending moment diagram of the beams of moment-resisting frames typically has the shape shown in Fig. 6.8. At the ULS this implies that Both the positive and negative plastic bending moments of the beam section are reached at the beam ends. 8 A complete reversal of moments takes place across the interior joints. the beam-column connection zone must be designed for the ability to transfer these large action effects due to these moments to ensure this, it is...

Confinement reinforcement in the critical regions of columns and ductile walls

The longitudinal reinforcement of columns and walls is normally symmetric, p, p2. So, the Clauses value of i0 specified via equations D5.ll for the plastic hinges cannot be provided as in 5.4.3.2.2 7 , beams, i.e. by keeping the extreme concrete fibres below their ultimate strain through a low 5.4.3.2.2 8 , difference between the tension and compression reinforcement ratios, px - p2 cf. equation 5.4.3.4.2 2 , D5.23 . In columns and walls we let, instead, the extreme concrete fibres reach their...

Regularity in plan

Regularity in plan influences essentially the choice of the structural model. The reasoning Clause 4.2.3.2 behind the provisions of EN 1998-1 in this respect is that structures that are regular in plan tend to respond to seismic excitation along their main structural directions in an uncoupled manner. Accordingly, for the design of regular structures in plan it is acceptable to analyse them in a simplified way, using planar models in each main structural direction. 4.3.2.1. Criteria for...

Design concepts design for strength or for ductility and energy dissipation ductility classes

Clause 5.2.1 As already mentioned in Section 2.2.2, Eurocode 8 gives the option to design concrete buildings for more strength and less ductility, or vice versa. This option is exercised through the ductility classification of concrete buildings Eurocode 8 permits trading ductility and dissipation capacity for strength by providing for three alternative ductility classes low DCL , medium DCM and high DCH . Buildings of DCM or DCH have q factors higher than the value of 1.5 considered to be...

Types of structural systems for earthquake resistance of concrete buildings

Section 5 identifies the following types of structural systems for concrete buildings, depending Clauses 5.1.2, on how the system responds to the horizontal components of the seismic action 5.2.2.1 8 'Torsionally flexible' systems 'Wall' systems of coupled or uncoupled walls 'Dual systems' of frames and walls 'Systems of large lightly reinforced walls'. The seismic response and performance of the first two types of systems has certain undesirable features. Consequently, these two types of...

Implementation of capacity design of concrete frames against plastic hinging in columns

The left-hand side of equation D4.23 Clause 5.2.3.3 2 The design value of the flexural capacity of a beam in negative hogging bending may be where Asl and As2 Asl gt As2 are the cross-sectional areas of the top and bottom reinforcement, respectively, b is the width of the web, d is the effective depth of the section, d2 is the distance of the centre oiA lt 2 from the bottom of the section, and cd and yd are the design strengths of steel and concrete, respectively. In the very uncommon...

Global and local ductility through capacity design and member detailing overview

As already noted in Section 4.11.2.2, to achieve a value of the global displacement ductility Clause 5.2.3 factor, that corresponds according to equations D2.1 and D2.2 to the value of the q factor used in the design of multi-storey buildings, a stiff and strong vertical spine should be provided up the height of the building, to spread the inelastic deformation demands throughout the structural system. As shown in Figs 4.4b and 4.4d, in concrete buildings this is accomplished either by using a...

Steel beams composite with a slab

Ductility condition for steel beams with a slab under a sagging positive moment The ductility condition for steel beams with a slab subjected to sagging moments complies with the general objective of achieving ductile dissipative zones with a reliable resistance the integrity of concrete is maintained during the design seismic event and yielding takes place in the steel section and or in the rebars. The problem of ductility appears only if the concrete might reach its crushing strain in...

Detailing of plastic hinge regions for flexural ductility

Deformation and ductility capacity depends not only on the detailing of members but on the Clauses 5.3.2, inherent ductility of their materials as well. Local deformation and ductility demands 5.4. I.I, 5.5.1.1 increase as the ductility class and with it the value of q increases. As a result, ductility requirements on materials increase with the ductility class. Because concrete strength positively affects member ductility and energy dissipation capacity in practically every respect from the...

Alternative representations of the seismic action

Time-history representation Clauses There are three approaches to obtain earthquakes or earthquake-like ground motion 3.2.3.1.1 1 , records acceleration versus time functions for the purposes of assessment by advanced 3.2.3.1.1 3 analysis. Natural records of earthquakes have increased exponentially in the past decade or so, leading to the availability of high-quality strong-motion acceleration data for different locations around the world, archived by many agencies. Another approach is...