Evaluating the effects of loading protocol on the strength and deformation capacity of Flexure-Shear critical concrete columns > 기술자료실

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Evaluating the effects of loading protocol on the strength and deformation

capacity of Flexure-Shear critical concrete columns

Seyed Sasan Khedmatgozar Dolati *, Adolfo Matamoros , Wassim Ghannoum

Department of Civil and Environmental Engineering, University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA

A R T I C L E I N F O

Keywords:

Finite element

Reinforced concrete

Columns

Loading effects

A B S T R A C T

Columns are considered critical elements with respect to the stability of buildings during earthquakes. Concrete

columns with light confinement can sustain shear and axial load failures, which can lead to partial or complete

building collapse. Moreover, tests have indicated that lateral cycling of non-ductile columns can impart damage

that is cumulative. However, most experiments on concrete columns have used fully reversed cyclic loading

protocols, while earthquake ground motions tend to impart different types of lateral histories. Due to a lack of

experimental evidence considering the effects of lateral loading protocols on the strength and deformation capacity

of reinforced concrete columns, nonlinear continuum finite element models were calibrated to experimental

tests for seven columns subjected to varying lateral loading protocols. Selected columns sustained

flexural-shear modes of lateral strength degradation. Columns were selected to cover a range of shear stresses,

cross-section, axial loads, transverse reinforcement spacing and ratios, and longitudinal reinforcement ratios. All

tested columns sustained axial collapse after cumulative damage from lateral loading. Calibrated column models

were then subjected to a series of loading protocols, including monotonic pushover and fully reversed cyclic

loading protocols with varying number of cycles. The effects of the lateral loading protocols on damage progression,

strength, and deformation capacities are discussed for the columns in light of differences in peak lateral

strength, drift at peak lateral strength, drift at the initiation of lateral strength degradation, and drift at the

initiation of axial strength degradation.

1. Introduction

Many older reinforced concrete buildings have poor seismic detailing

and particularly columns with light confinement ([1,2,3]). When such

buildings are subjected to high-intensity earthquake loads, severe

damage can occur, as well as collapse ([4]). In fact, older non-ductile

concrete buildings are often the major source of deaths in earthquakes

([5,6,7,8]). Literature shows that the collapse of reinforced concrete

buildings in major earthquakes is typically associated with loss of

gravity-load carrying capacity of vertical members such as columns and

walls ([5,6,9]).

Experimental tests demonstrate that the behavior of concrete columns,

particularly at large damage states, is considerably affected by the

magnitude and history of lateral and axial loading ([10,11]). Nonductile

concrete columns can collapse due to high axial load, high

lateral displacement, or a combination of both. Experimental investigations

have shown that a column, which has been adequately

designed to resist gravity loads, experiences axial failure usually when

shear resistance degrades significantly [12]. In a test by Lynn [13], axial

failure occurred after a significant loss of lateral load resistance.

Experimental tests indicate that the flexural strength and displacement

capacity of columns under variable axial force were completely different

([14,15]). Tests by Melek et al. [16] indicate that the envelope of lateral

load versus lateral displacement relations depends on the axial load level

on columns. In tests by Ousalem [17], it is found that columns with

higher axial load experience more rapid strength degradation than those

with low axial load. In addition, the post-peak strength degradation

behavior was shown to be highly dependent on loading history. These

tests indicate that the lateral drift at which axial collapse occurs in tests

with lateral-drift cycles can be less than half that of columns pushed

monotonically in one direction ([10,11,18]). Experimental investigations

have shown that the flexural capacity of the section

considering loading history in some level of the axial load was significantly

less than the value calculated without considering loading history

([14,19]). In tests by Goodnight et al. [20], it is found that the symmetric

three-cycle set load history is more severe than the displacement history