Outline

  • Abstract
  • Introduction
  • Center of Rigidity
  • Review of Goel and Chopra’s Approach to Rigid Floor Diaphragm
  • Analysis for Buildings with Flexible Floor Diaphragms
  • Procedure with All Floor Definition
  • Procedure with Single Floor Definition
  • Illustration of Methodology
  • Summary and Conclusions
  • References

رئوس مطالب

  • چکیده
  • مقدمه
  • مرکز صلبیت
  • نقد و بررسی رویکرد گوئل و کوپرا برای دیافراگم طبقه صلب
  • تحلیلی برای ساختمانهای دارای طبقه انعطف پذیر
  • نمایش متدولوژی
  • خلاصه و نتیجه گیری ها

Abstract

Even though a rigid floor diaphragm is a good assumption for seismic analysis of most buildings, several building configurations may exhibit significant flexibility in floor diaphragm. However, the issue of static seismic analysis of such buildings for torsional provisions of codes has not been addressed in the literature. Besides, the concept of center of rigidity needs to be formulated for buildings with flexible floor diaphragms. In this paper, the definition of center of rigidity for rigid floor diaphragm buildings has been extended to unsymmetrical buildings with flexible floors. A superposition-based analysis procedure is proposed to implement code-specified torsional provisions for buildings with flexible floor diaphragms. The procedure suggested considers amplification of static eccentricity as well as accidental eccentricity. The proposed approach is applicable to orthogonal as well as nonorthogonal unsymmetrical buildings and accounts for all possible definitions of center of rigidity.

Keywords: - - -

Summary and Conclusions

In seismic analysis of buildings, the floor slab is usually assumed to be rigid in its own plane. However, for many buildings that are long and narrow or have stiff end walls, floor diaphragm flexibility must be accounted for in the distribution of lateral load. Considerable research has been reported in the literature on the dynamics of flexible floor diaphragm buildings; however, the issue of seismic design of such buildings that takes into consideration torsional provisions of the codes has not yet been addressed. In this paper we developed a framework for analysis of such buildings following usual codal requirements for torsion. The building is assumed to have a single wing only, i.e., buildings with multiple wings ~e.g., L, V, Y, etc. shaped! are not considered.

The definition of center of rigidity for rigid floor diaphragm buildings is extended to flexible floor buildings. The no-torsion condition for flexible floor buildings is defined such that center nodes at either end of the diaphragm are constrained so that they undergo equal horizontal displacement. The proposed analysis procedure considers the final response as the superposition of three cases: the no-torsion case, amplification of the static eccentricity, and accidental torsion. The proposed procedure ensures that the resultant member force is close to that of rigid floor buildings as the floor diaphragm rigidity increases.

Analysis results of a sample building clearly show the significance of considering the torsion provisions of design codes for asymmetric flexible diaphragm buildings. It is seen that treating the diaphragms of such buildings as rigid for torsional analysis may cause considerable error. The example also illustrates that the contribution of accidental torsion as well as the torsional amplification terms can be quite significant. However, the usual codal specification of accidental eccentricity as a fraction of the building dimension may be somewhat conservative for such buildings and this issue needs to be addressed in the future.

Horizontal offset buildings constitute a class of structures that are particularly prone to in-plane floor deformation and torsion occurring simultaneously. The present work may be useful for developing a methodology for the treatment of such buildings.

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