## When A Live Load Is Considered Quasi Permanent

-A/bd=0.5 total deflection -A/bd=0.5 active deflection A/bd=1.5 total deflection A/bd=1.5 active deflection

humidity

Figure 7.21. Influence of relative humidity on Slenderness Limits for Total and Active Deflections (referred to 70% RH)

From Fig. 7.21 it can be seen that the influence of relative humidity on the slenderness ratio is important with a variation of ±15% for the active deflection and ±10% for total deflection from the reference value of 70% of relative humidity.

The figure also shows that the influence of relative humidity does not significantly depend on the steel reinforcement ratio.

For this study, different load distributions have been assumed, including the assumption that the quasi permanent service load, qcp, can be taken as 0.5 times the ultimate limit state (ULS) load. The ULS load is given by the following expression:

As explained in section 7.4.3.3, the ultimate load quLs is known from the value of the reinforcement. If it is assumed that gi « 1.5- g2, then by fixing different values for the quasi permanent service load (qcp)/ultimate load (quLs) ratio, gi, gi and q may be determined for each ratio. This provides, in the end, significantly different values for the permanent to live load ratios for the quasi permanent combination. The lower the value of the permanent load, the lower will be the load considered for the verification of deflections, since only 30% of the live load is considered quasi permanent. In Table 7.7, the different ratios of qcp/quLs considered and the resulting ratios of gi/qtot, g2/qtot and q/qtot are given.

 flrtfc s (h/t},* p 0/£>™ Q/Ct,<„ 46% 30% 20% 50% 51% 36% 24% 40% 57% 42% 28% 30% 59% 45% 30% 25% 63% 54% 36% 10%

The comparison of the results of the slenderness limits for the different quasi permanent service load to ultimate load ratios is plotted in Fig. 7.22. As can be seen the difference is important. It is also interesting to note that the values of l/d = 20 for 0.5% reinforcement ratio and l/d= 14 for 15% reinforcement ratio, are obtained approximately for a ratio of qcp/quLs=0.5.

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### Responses

• Niklas
When a live load is considered quasi permanent?
9 months ago
• roosa
What is quasi permanent combination?
6 months ago
• Eleanor