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CONTENTS
Volume 16, Number 4, October 2015
 

Abstract
Traditionally, multi-story buildings are designed to provide stiffer structural support to withstand lateral earthquake loading. Introducing flexible elements at the base of a structure and providing sufficient damping is an alternative way to mitigate seismic hazards. These features can be achieved with a device known as an isolator. This paper covers the design of base isolators for multi-story buildings in medium-risk seismicity regions and evaluates the structural responses of such isolators. The well-known tower building for police personnel built in Dhaka, Bangladesh by the Public Works Department (PWD) has been used as a case study to justify the viability of incorporating base isolators. The objective of this research was to establish a simplified model of the building that can be effectively used for dynamic analysis, to evaluate the structural status, and to suggest an alternative option to handle the lateral seismic load. A finite element model was incorporated to understand the structural responses. Rubber-steel bearing (RSB) isolators such as Lead rubber bearing (LRB) and high damping rubber bearing (HDRB) were used in the model to insert an isolator link element in the structural base. The nonlinearities of rubber-steel bearings were considered in detail. Linear static, linear dynamic, and nonlinear dynamic analyses were performed for both fixed-based (FB) and base isolated (BI) buildings considering the earthquake accelerograms, histories, and response spectra of the geological sites. Both the time-domain and frequency-domain approaches were used for dynamic solutions. The results indicated that for existing multi-story buildings, RSB diminishes the muscular amount of structural response compared to conventional non-isolated structures. The device also allows for higher horizontal displacement and greater structural flexibility. The suggested isolation technique is able to mitigate the structural hazard under even strong earthquake vulnerability.

Key Words
structural retrofitting; seismic isolation; existing building; rubber-steel bearing; frequency domain; time domain analysis; LRB; HDRB; innovative model

Address
A.B.M. Saiful Islam, Mohd Zamin Jumaat, Md. Akter Hosen and Md. Nazmul Huda: Department of Civil Engineering, University of Malaya, Kuala Lumpur, Malaysia
Raja Rizwan Hussain: CoE-CRT, Department of Civil Engineering, College of Engineering, King Saud University, Riyadh, Saudi Arabia

Abstract
The objective of this study was to examine the effect of repair mortar on the dynamic properties such as natural frequencies, mode shape and damping ratios of two story single span scale reinforced concrete building. To this end, two story single span scale reinforced concrete building having dimensions of 150 cm (width), 150 cm (length) and 135 cm (height) was constructed. Workmanship defects such as separation of aterial, faulty vibration application and bad gradation of the structure were properly evaluated. Dynamic properties of damaged structure were experimentally determined using Operational Modal Analysis (OMA). Detected defects in the structure were fixed by plastering with repair mortar. Dynamic properties of repaired structure were reevaluated by using the OMA method. Finite element software called Abaqus was used to numerically determine dynamic properties of the structure. Structure modeled as solid was subjected to Linear Perturbation Frequency Method. The changes in dynamic properties of structure after the repair process were comparatively studied by evaluating experimental and numerical results.

Key Words
dynamic properties; operational modal analysis; abaqus; concrete building; repair

Address
Hakan Basaran: Department of Civil Engineering, Celal Bayar University, Manisa, Turkey

Abstract
High Performance Fiber Reinforced Cementitious Composites which are called HPFRCC, include cement matrices with strain hardening response under tension loading. In these composites, the cement mortar with fine aggregates, is reinforced by continuous or random distributed fibers and could be used for various applications including structural fuses and retrofitting of reinforced concrete members etc. In this paper, mechanical properties of HPFRCC materials are reviewed briefly. Moreover, a reinforced concrete beam (experimentally tested by Maalej et al.) is chosen and in different specimens, lower or upper or both parts of that beam are replaced with HPFRCC layers. After modeling of specimens in ABAQUS and calibration of those, mechanical properties of these specimens are investigated with different thicknesses, tensile strengths, tensile strains and compressive bars. Analytical results which are obtained by nonlinear finite analyses show that using HPFRCC layers with different parameters, increase loading capacity and ultimate displacement of these beams compare to RC specimens.

Key Words
beam; HPFRCC; nonlinear finite element; reinforced concrete; ultimate load; ultimate displacement

Address
Ali Hemmati:Department of Civil Engineering, Semnan Branch, Islamic Azad University, Semnan, Iran
Ali Kheyroddin: Civil Engineering Faculty, Semnan University, Iran and Visiting Scholar in Department of Civil Engineering and Applied Mechanics, University of Texas, Arlington, TX, USA
Mohammad K. Sharbatdar: Civil Engineering Faculty, Semnan University, Semnan, Iran


Abstract
Various computational tools are available for modeling highly nonlinear structural engineering problems that lack a precise analytical theory or understanding of the phenomena involved. This paper adopts a fairly simple nonparametric adaptive regression algorithm known as multivariate adaptive regression splines (MARS) to model the nonlinear interactions between variables. The MARS method makes no specific assumptions about the underlying functional relationship between the input variables and the response. Details of MARS methodology and its associated procedures are introduced first, followed by a number of examples including three practical structural engineering problems. These examples indicate that accuracy of the MARS prediction approach. Additionally, MARS is able to assess the relative importance of the designed variables. As MARS explicitly defines the intervals for the input variables, the model enables engineers to have an insight and understanding of where significant changes in the data may occur. An example is also presented to demonstrate how the MARS developed model can be used to carry out structural reliability analysis.

Key Words
multivariate adaptive regression splines; structural analysis; nonlinearity; basis function; neural networks

Address
Wengang Zhang and A.T.C. Goh: School of Civil & Environmental Engineering, Nanyang Technological University, Block N1, Nanyang Avenue, 639798, Singapore

Abstract
The hybrid-type penalty method (HPM) is suitable for representing failure phenomena occurring during the transition from continua to discontinua in materials such as concrete. Initiation and propagation of dominant cracks and branching of cracks can easily be modeled as a discrete crack. The HPM represents a discrete crack by eliminating the penalty that represents the separation of the elements at the intersection boundary. This treatment is easy because no change in the degrees of freedom for the discrete crack is necessary. In addition, it is important to evaluate the correct deformation of the continua before the crack formation is initiated. To achieve this, we implemented a constitutive model of concrete for the HPM. In this paper, we explain the implemented constitutive model and describe the simulation of an anchor bolt pullout test using the HPM demonstrating its capability for evaluating progressive failure

Key Words
hybrid-type penalty method; discrete crack; concrete structure

Address
Yoshihiro Fujiwara: Graduate School of Engineering and Design, Hosei University
Norio Takeuchi: Graduate School of Engineering and Design, Hosei University, 2-33 Ichigaya Tamachi, Shinjuku, Tokyo 162-0843, Japan
Tadahiko Shiomi: Mind Inc., 7-17-19 Maebara-nishi Funabashi Chiba 274-0825, Japan
Atsushi Kambayashi: Research & Development Institute, Takenaka Corporation, 1-5-1 Ohtsuka, Inzai, Chiba 270-1395, Japan


Abstract
A coupled experimental and numerical study of shear fracture in the edge-notched beam specimens of quasi-brittle materials (concrete-like materials) are carried out using four point bending flexural tests. The crack initiation, propagation and breaking process of beam specimens are experimentally studied by producing the double inclined edge notches with different ligament angles in beams under four point bending. The effects of ligament angles on the shear fracturing path in the bridge areas of the double edge-notched beam specimens are studied. Moreover, the influence of the inclined edge notches on the shear-fracture behavior of double edge-notched beam specimens which represents a practical crack orientation is investigated. The same specimens are numerically simulated by an indirect boundary element method known as displacement discontinuity method. These numerical results are compared with the performed experimental results proving the accuracy and validity of the proposed study.

Key Words
inclined edge notches; concrete like specimens; crack propagation; indirect shear loading; shear-fracture behavior

Address
Hadi Haeri: Department of Mining Engineering, Bafgh Branch, Islamic Azad University, Bafgh, Iran

Abstract
Prestressed concrete bridges with corrugated steel webs have emerged as one of the promising bridge forms. This structural form provides excellent structural efficiency with the concrete flanges primarily taking bending and the corrugated steel webs primarily taking shear. In the design of this type of bridges, the flexural ductility and deformability as well as strength need to be carefully examined. Evaluation of these safety-related attributes requires the estimation of full-range behaviour. In this study, the full-range behaviour of beam sections with corrugated steel webs is evaluated by means of a nonlinear analytical method which uses the actual stress-strain curves of the materials and considers the path-dependence of materials. In view of the different behaviour of components and the large shear deformation of corrugated steel webs with negligible longitudinal stiffness, the assumption that plane sections remain plane may no longer be valid. The interaction between shear deformation and local bending of flanges may cause additional stress in flanges, which is considered in this study. The numerical results obtained are compared with experimental results for verification. A parametric study is undertaken to clarify the effects of various parameters on ductility, deformability and strength.

Key Words
corrugated steel web; ductility and deformability; flexural strength; partially prestressed concrete; reinforced concrete

Address
X.C. Chen, F.T.K. Au, Z.Z. Bai, Z.H. Li and R.J. Jiang:Department of Civil Engineering, The University of Hong Kong, Hong Kong, China


Abstract
3-dimentional precast recycled aggregate concrete (RAC) finite element models were developed by means of the platform OpenSees to implement sophisticated nonlinear model subjected to seismic loads. Efforts were devoted to the dynamic responses (including dynamic characteristics, acceleration amplifications, displacements, story drifts) and capacity curve. In addition, this study extended the prediction on dynamic response of precast RAC model by parametric study of material properties that represent the replacement percentage of Recycled Coarse Aggregate (RCA). Principles and assumptions that represent characteristics of precast structure and influence of the interface between head of column and cast-in-place (CIP) joint on the stiffness of the joints was put forward and validated by test results. As a result, the comparison between simulated and tested results of the precast RAC frame shows a good correlation with most of the relative errors about 25% in general. Therefore, the adopted assumptions and the platform OpenSees are a viable approach to simulate the dynamic response of precast frames made of RAC.

Key Words
recycled aggregate concrete (RAC); precast frame; dynamic responses; dynamic nonlinear analysis; simulated result; tested result; interface

Address
ThiLoan Pham, Jianzhuang Xiao and Tao Ding: Department of Structural Engineering, Tongji University, Shanghai, 200092, PR China

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