Numerical Investigation of Variable Length of Seismic Damage Region for Reinforced Concrete Columns

ABSTRACT

The seldom investigation of variable length of damage region prevents the estimation of probabilistic drift limits of reinforced concrete columns at different performance levels for the performance-based seismic design. However, if using the numerical approach to predict the variability of damage region within the framework of force-based beam-column element, the current force-based beam-column element is unable to model the spreading of damage region. Therefore, a new numerical simulation method is proposed to compute the emergence, propagation and termination of damage region of reinforced concrete columns. Then, based on the developed numerical simulation method, the measured response of experimental testing is calibrated. From the calibration, it can be observed that there is a rapid increase on the variable length of damage region with the increasing of lateral displacement and then followed by a stable stage. The propagation of the longitudinal reinforcement yielding and concrete tensile cracking mainly occurs in the ascending branch of the load–displacement response. Then, based on the growth characteristic of the damage region from the numerical simulation, an empirical equation is proposed to describe the variable length of damage region by using the least-square regression analysis to fit the computed responses for its simplicity to use in engineering practices. Finally, the stable length of damage region is reinvestigated by carrying out a parametric study with the developed numerical simulation method, indicating that two critical design parameters, specifically the axial load ratio and the shear span ratio, have considerable influences on this quantity of interest.     

Development and Seismic Behavior of Precast Concrete Beam-to-Column Connections

A new precast concrete beam-to-column connection for moment-resisting frames was developed in this study. Both longitudinal bar anchoring and lap splicing were used to achieve beam reinforcement continuity. Three full-scale beam-to-column connections, including a reference monolithic specimen, were investigated under reversal cyclic loading. The difference between the two precast specimens was the consideration of additional lap-splicing bars in the calculation of moment-resisting strength. Seismic performance was evaluated based on hysteretic behavior, strength, ductility, stiffness, and energy dissipation. The plastic hinge length of the specimens is also discussed. The results show that the proposed precast system performs satisfactorily under reversal cyclic loading compared with the monolithic specimen, and the additional lap-splicing bars can be included in the strength calculation using the plane cross-section assumption. Furthermore, the plastic hinge length of the proposed precast beam-to-column connection can be estimated using the models for monolithic specimens.     

Earthquake-Induced Damage Detection in a Monumental Masonry Bell-Tower Using Long-Term Dynamic Monitoring Data

ABSTRACT

This work investigates the use of an advanced long-term vibration-based structural health monitoring tool to automatically detect earthquake-induced damages in heritage structures. Damage produced in a monumental bell-tower at increasing values of the Peak Ground Acceleration (PGA) of the seismic input is predicted by incremental nonlinear dynamic analysis, using a Finite Element model calibrated on the basis of experimentally identified natural modes. Then, predicted damage effects are artificially introduced in the monitoring data to check for their detectability. The results demonstrate that a very small damage, associated to a low intensity and low return period earthquake, is clearly detected by the monitoring system.     

Modeling and Seismic Response Analysis of Italian Code-Conforming Reinforced Concrete Buildings

ABSTRACT

This study investigates the seismic response of reinforced concrete buildings designed according to the current Italian building code. Number of stories, site hazard, presence and distribution of masonry infill panels, and type of lateral resisting system are the key investigated parameters. The main issues related to design and modeling are discussed. Two Limit States are considered, namely Global Collapse and Usability-Preventing Damage. The main aim of the study is a comparison between the seismic response of the buildings, investigated through nonlinear static and dynamic analyses. Irregularity in the distribution of infill panels and site hazard emerge as the most influential parameters.     

Flexural and Shear Damage Models for MRF Structures Excited by Far-Field Horizontal Strong Ground Motions

The unexpected damages in structures during severe earthquakes have been reported frequently so far. In this study, the damage-based inelastic behavior of special moment resisting frame (SMRF) structures designed according to the new versions of general earthquake loading codes (International building code [IBC] 2012 & American Society of Civil Engineers [ASCE] 7-2010) and seismic design references (National Earthquake Hazards Reduction Program [NEHRP] 2009 & Federal Emergency Management Agency [FEMA] P-750) has been investigated. The final results presented based on distinctive shear and flexural failure modes show that a non-uniform distribution of severe damage in structural height occurs during design level seismic excitations. Also it is observed that the shear and flexural damages are more critical in short and tall MRF structures, respectively.     

Modeling the Seismic Response of Modern URM Buildings Retrofitted by Adding RC Walls

Modern unreinforced masonry buildings with reinforced concrete slabs are often retrofitted by inserting reinforced concrete walls. The main advantages of this technique are the increase in strength and displacement capacity with respect to masonry structures. This article presents two modeling approaches for evaluating such structures: a shell-element model and a macro-element one. The objective is to formulate practical recommendations for setting up a macro-element model using as input the geometry of the structure and results from standard material tests. Structural configurations of masonry buildings, in which the insertion of reinforced concrete walls is an efficient retrofit technique, are also investigated.     

Strength Hierarchy at Reinforced Concrete Beam-Column Joints and Global Capacity

Strength hierarchy assessment is a method that can be utilized to identify the weakest structural element at a reinforced concrete (RC) beam-column joint. The method was extensively used in various research activities at the University of Canterbury, which mainly involved beam-column joint subassembly tests. However, this method required improvements and refinements in order to be adopted in multi-story building applications. In this paper, the improvements made to the method are reported. In the improved method, capacity of the weakest element at every beam-column joint in an RC frame building can be related to the corresponding global base shear demand. The method has been illustrated via two example applications: an RC frame lacking joint shear reinforcement and a modern RC frame with adequate joint shear reinforcement. The case study examples confirmed the accuracy and the effectiveness of the method.     

Concreting the frontier: Modernity and its entanglements in Sikkim,India

Sikkim is a geopolitically sensitive frontier state in India sharing borders with Bhutan, China and Nepal. As distinctions between urban and rural dissolve across the Himalaya, concrete narrates the transformation of these landscapes and the assemblages that hold them together. Using Cloke and Jones’s (2001) notion of ‘dwelling’ we explore Sikkim's concrete manifested in tourism, hydropower and housing to make four arguments. First, concrete is central to the way development is conceived and enacted in Sikkim and offers a critical reading of the ways landscape is imagined, reproduced and politicised. Second, concrete foregrounds the ways peoples' aspirations are materialised in the built environment of a ‘remote’, yet geopolitically significant territory. Third, concrete is an integral component of Sikkim's political culture, part of the assemblage of incongruent elements that undergird the state's dependency. Finally, concrete has further entangled Sikkim within India, producing a loyal border state out of a recently independent polity.     

Modeling and Seismic Response Analysis of RC Precast Italian Code-Conforming Buildings

ABSTRACT

In this study, industrial single-story RC precast buildings are investigated. Twenty-four case studies have been considered, in which the column height, the beam spans and the seismic hazard level are varied. The seismic design of the selected case studies is performed according to the Italian building code and additional technical documentation. Three-dimensional nonlinear models are defined to perform static and dynamic analyses for the seismic assessment of the selected case studies. Demand/capacity ratios in terms of the selected engineering demand parameters are computed for ten increasing values of the seismic input return period.     

Seismic Behavior of RC Bridge Piers under Bidirectional Excitations: Implications of Site Effects

Seismic demand of structures may be potentially magnified due to bidirectional shaking. This may also be strongly influenced by the amplification and/or attenuation of motions due to local site conditions. Current investigation examines the implications of these two aspects collectively. A code-designed reinforced concrete pier has been analyzed under recorded accelerograms and their derivatives from 1-D site analysis. Magnification in peak and cumulative responses due to bidirectional shaking may be sensitive to record-to-record variability. However, such magnification remains relatively stable across site characteristics. Combination rules are shown adequate to estimate peak deformation and deficient for cumulative demand irrespective of the site conditions.