Khalid M. Mosalam

Performance of reinforced concrete buildings during the August 17, 1999 Kocaeli, Turkey earthquake, and seismic design and construction practise in Turkey

Abstract A large number of reinforced concrete buildings collapsed or were heavily damaged during the 7.4 magnitude earthquake that struck northwestern Turkey on August 17, 1999. Recorded peak ground accelerations were relatively low (0.3 g–0.4 g) compared to the magnitude of the structural damage, and the elastic acceleration response spectra from the recorded motions were comparable with the elastic design spectra specified in the current Turkish seismic code. Seismic code requirements are discussed and compared with observed details. Many structural deficiencies were highlighted by the earthquake damage, including: reinforced concrete columns with insufficient confinement and transverse reinforcement, 90-degree hooks at the end of column ties, poor detailing in beam-column joint regions, strong-beam and weak-columns, soft and weak stories, and poor quality construction. Buildings with shear wall structural elements generally performed well.

PROBABILISTIC SEISMIC DEMAND MODELS AND FRAGILITY ESTIMATES FOR RC BRIDGES

A Bayesian methodology to construct probabilistic seismic demand models for the components of a structural system is developed. Existing deterministic models and obserational data are used. The demand models are combined with previously developed capacity models for reinforced concrete (RC) bridge columns to estimate the seismic fragilities of bridge components and systems. The approach properly accounts for all relevant uncertainties, including model error. Application to two bridge examples typical of modern California practice is presented.

Strengthening of two-way concrete slabs with FRP composite laminates

Abstract This paper presents an experimental and analytical investigation for evaluating the ultimate response of unreinforced and reinforced concrete slabs repaired and retrofitted with fiber reinforced polymer (FRP) composite strips. A uniformly distributed pressure was applied to several two-way large-scale slab specimens using a high-pressure water bag. Both carbon/epoxy and E-glass/epoxy composite systems were used in this study. In predicting the behavior of the repaired slabs, the finite element method was used. Comparison between the experimental and the analytical results indicated the validity of the computational models in capturing the experimentally determined results for both the control and the rehabilitated slabs. For repair applications, test results indicated that both FRP systems were effective in appreciably increasing the strength of the repaired slabs to approximately five times that of the as-built slabs. For retrofitting applications, use of FRP systems resulted in appreciable upgrade of the structural capacity of the as-built slabs up to 500% for unreinforced specimens and 200% for steel reinforced specimens.

Nonlinear transient analysis of reinforced concrete slabs subjected to blast loading and retrofitted with CFRP composites

Abstract Computational models using the finite element method for nonlinear transient analysis of reinforced concrete (RC) two-way slabs subjected to blast loading are presented. Both as-built and retrofitted slabs with carbon fiber reinforced polymer (CFRP) composite strips are analyzed. The models are used to investigate different parameters including (a) loading duration, and (b) effect of CFRP retrofit on damage accumulation. In this study, damage is globally quantified by the amount of reduction of the first two vibrational frequencies of the slabs. Local representation of damage in terms of reinforcing steel strains is also discussed. The computational models for both the as-built and the retrofitted slabs are verified using experimental results. In these experiments, a slowly increasing uniform pressure is applied to the bottom surface of large-scale RC slab specimens using high-pressure water bag. Experimental results showed that an increase up to 200% in the load carrying capacity is achieved when using the CFRP composite retrofit system. Transient nonlinear analysis results proved the efficiency of the CFRP composite retrofit in improving the slab behavior under blast loading for different loading durations, i.e. for small, medium, and large charge weights at the same applied maximum pressure. In particular, less than 50% reduction of the fundamental frequency due to concrete damage is obtained for the retrofitted slab compared to more than 85% reduction for the as-built slab. Moreover, the maximum displacement is reduced by 40–70% with the CFRP retrofit compared to the as-built slab. As for reinforcing steel strains, the application of CFRP retrofit significantly limited the spread of yielding in time and space. The improved slab behavior with CFRP is best when retrofitting is applied to both sides of the slab.

SEISMIC FRAGILITY OF LRC FRAMES WITH AND WITHOUT MASONRY INFILL WALLS

This paper summarises the first phase of the fragility analyses of generic (representative) buildings in the area of Memphis, Tennessee, USA. The study was conducted at Cornell University as a part of the project Loss Assessment of Memphis Buildings (LAMB) for the National Center for Earthquake Engineering Research (NCEER). In this study, the fragility analyses focus on low-rise Lightly Reinforced Concrete (LRC) frame buildings with and without infill walls. The obtained fragility curves are compared with those of ATC-13 for different facility classes. Based on the obtained fragility curves, it is concluded that adding masonry infill walls to low-rise LRC frame buildings significantly reduces the likelihood of seismic damage.

PEER Performance-Based Earthquake Engineering Methodology, Revisited

A performance-based earthquake engineering (PBEE) methodology was developed at the Pacific Earthquake Engineering Research (PEER) Center. The method is based on explicit determination of performance, e.g., monetary losses, in a probabilistic manner where uncertainties in earthquake ground motion, structural response, damage, and losses are explicitly considered. There is an increasing trend towards use of probabilistic performance-based design (PPBD) methods in practice. Therefore, the International Federation for Structural Concrete (fib) initiated a task group to disseminate PPBD methods. This article is a contribution to this task group summarizing and demonstrating the PEER PBEE methodology in a useful manner to practicing engineers.

RESPONSE OF INFILLED FRAMES USING PSEUDO-DYNAMIC EXPERIMENTATION

SUMMARY An accurate and practical testing technique to study seismic performance of multi-storey infilled frames is formulated. This technique is based on the pseudo-dynamic method which can provide an acceptable approximation of the dynamic performance of structures under the influence of earthquake excitation. The pseudo-dynamic experimental technique is outlined and applied for testing a two-bay, two-storey gravity load designed steel frame infilled with unreinforced concrete block masonry walls. From the discussion of the results, the dynamic performance of the tested structure is assessed. ( 1998 John Wiley & Sons, Ltd. Pseudo-dynamic experimentation is a testing procedure in which the dynamic response of the structure is calculated and the obtained displacements are statically applied to the structure in an on-line procedure. This technique is essentially identical to traditional time domain analysis but rather than idealizing the non-linear sti⁄ness characteristics of the structure, the static restoring forces are directly measured from the specimen as the experiment proceeds. Computation of displacements is based on numerical integration of the governing second-order di⁄erential equations of motion of a system with assumed mass and damping properties and with a forcing function corresponding to a selected dynamic loading. During the test, actual displacements and restoring forces are measured using equipment normally used for static experiments. These measured quantitites are utilized in subsequent calculations. In this way, both dynamic e⁄ects and progressive damage of the specimen are included in the imposed displacements, and the procedure allows for an in-depth monitoring of the performance of the structure for the entire duration of realistic earthquake excitation. Infilled frames have been investigated experimentally by many researchers, most often with monotonic (see e.g. Reference 1) or quasi-static cyclic loading (see e.g. Reference 2), and in a few cases with actual dynamic

Progressive Collapse Analysis of Reinforced Concrete Frames with Unreinforced Masonry Infill Walls Considering In-Plane/Out-of-Plane Interaction

Reinforced concrete (RC) frames with unreinforced masonry (URM) infill walls are commonly used in seismic regions around the world. It is recognized that many buildings of this type perform poorly during earthquakes. Therefore, proper modeling of the infill walls and their effect on RC frames is essential to evaluate the seismic performance of such buildings and to select adequate retrofit methods. Using damage observations of RC buildings with URM infill walls from recent earthquakes, this paper presents a new approach to consider in-plane/out-of-plane interaction of URM infill walls in progressive collapse simulations. In addition, the infill wall effect to induce shear failure of columns is simulated with a nonlinear shear spring modeling approach. The research endeavor is accompanied by implementation of the developed modeling aspects in the publicly available open-source computational platform OpenSees for immediate access by structural engineers and researchers.

Experimental Investigation of Nonductile RC Corner Beam-Column Joints with Floor Slabs

AbstractThe paper presents the experimental investigation of full-scale RC corner beam-column joints without transverse reinforcement in the joint region leading to nonductile behavior in many exiting RC buildings. The experimental study considered two design parameters: joint aspect ratio and beam longitudinal reinforcement ratio. Four corner beam-column joint specimens were constructed with transverse beams and floor slabs and tested under quasi-static cyclic loading. The specimens experienced joint shear failure without beam hinging mechanism as a result of the absence of transverse reinforcement in the joint region. On the basis of the test results, the paper discusses the effects of these two design parameters and the floor slab on the behavior of corner beam-column joints. The joint shear strengths obtained from the test specimens are compared with the strength recommendations of the ASCE/SEI 41-06 provisions.

Evolutionary characteristic length method for smeared cracking finite element models

The fixed smeared crack concept with strain decomposition is reformulated utilizing a self-adaptive strategy at the constitutive level. This formulation focuses on continuous adaptation of the crack band width based on the incremental finite element solution and the idea of nonlocal continuum. The required nonlocal forms are obtained by means of the superconvergent patch recovery procedure. Comparison with experimental results indicates the superiority of the present formulation over the standard smeared cracking.