关于抗震设计的英文翻译

英文翻译

英文原文

Comparative Application of Capacity Models for Seismic

Vulnerability Evaluation of Existing RC Structures

Abstract. Seismic vulnerability assessment of existing buildings is one of

the most common tasks in which Structural Engineers are currently

engaged. Since, its is often a preliminary step to approach the issue of

how to retrofit non-seismic designed and detailed structures, it plays a

key role in the successful choice of the most suitable strengthening

technique. In this framework, the basic information for both seismic

assessment and retrofitting is related to the formulation of capacity

models for structural members. Plenty of proposals, often contradictory

under the quantitative standpoint, are currently available within the

technical and scientific literature for defining the structural capacity in

terms of force and displacements, possibly with reference to different

parameters representing the seismic response. The present paper shortly

reviews some of the models for capacity of RC members and compare

them with reference to two case studies assumed as representative of a

wide class of existing buildings.

Keywords: Assessment, Vulnerability, Capacity, Existing Structures,

Reinforced Concrete.

INTRODUCTION

Seismic assessment of existing RC structures is a cutting-edge issue

for structural engineers. The increased levels of safety required to new

structures by the last generation of codes of standards indirectly

emphasizes the lack in seismic performance usually affecting the existing

ones. Seismic vulnerability evaluation can be carried out according to

various code provisions about capacity of members of existing structures

under earthquake actions. Different damage measures can be adopted for

quantifying seismic capacity even depending on the type of structure

considered. Three different parameters, besides other less common

quantities, have been proposed for measuring seismic performance of

reinforced concrete structures.Indeed, plastic rotations are considered in

the U.S. code [6] for quantifying seismic capacity of beams and columns,

while the total chord rotation is assumed as capacity measures for RC

members in both the European [2] [3] and Italian [4] [5] seismic codes.

Other proposals can be found within the scientific literature and the

technical practice. For instance, the interstorey-drift angle is a parameter

commonly used for quantifying seismic capacity and demand on

structures [1]; furthermore, on the basis of particular assumptions about

the mechanism most likely to occur, interstorey drift values can be

somehow converted into global displacements [7]. According to the

general Performance-Level framework of the current codes, various levels of damage can be tolerated for every relevant Performance Level

of the structures. Consequently,they assume different threshold values, in

terms of the various measures mentioned above, for stating whether a

given structure attains or not the Limit States of interest in seismic design

and assessment. The present paper, after a critical review of the various

proposals for all the relevant Limit States, compares the various

definitions of structural capacity of members for two existing RC

structures, designed for gravitational loads, assumed as case-studies.

OUTLINE OF CAPACITY MODELS FOR RC MEMBERS

Several parameters and indices can be considered for measuring

structural performance under horizontal actions induced by earthquake

shaking. As a matter of principle, those parameters should look after the

cyclic nature of the seismic response. Park&Ang Damage Index,

Low-Cycle Fatigue Index [8] and other similar measures follow the cyclic

evolution of the structural response defining suitable threshold values of

the corresponding indices for defining the achievement of the relevant

Limit States.Although those parameters explicitly consider the actual

evolution of the structural response, they are not so easy to evaluate at

both local and global level. Consequently, capacity is more often defined

in terms of displacement parameters whose maximum value attained

during the seismic response is considered. Figure 1 shows the three different displacement measures which are more commonly considered

within the scientific and technical literature:

- the interstorey drift angle ID, which can be evaluated as ratio

between the intestorey relative displacement ij a the storey height

h;

- the plastic rotation pl which is defined as the concentrated rotation

which is equivalent to the plastic curvatures arising around the

column end throughout a length pll which is the length of the