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CONTENTS
Volume 47, Number 6, September25 2013
 

Abstract
Distributed-Steel Bar Reinforced Concrete (DSBRC) columns, a new and innovative construction technique for composite steel and concrete material which can alleviate the difficulty in the arrangement of the stirrup in the column, were studied experimentally and analytically in this paper. In addition, an ordinary steel Reinforced Concrete (SRC) column was also tested for comparison purpose. The specimens were subjected to quasi-static load reversals to model the earthquake effect. The experimental results including the hysteresis curve, resistance recession, skeleton curves and ductility ratio of columns were obtained, which showed well resistant-seismic behavior for DSBRC column. Meanwhile a numerical three-dimensional nonlinear finite-element (FE) analysis on its mechanical behavior was also carried out. The numerically analyzed results were then compared to the experimental results for validation. The parametric studies and investigation about the effects of several critical factors on the seismic behavior of the DSBRC column were also conducted, which include axial compression ratios, steel ratio, concrete strength and yield strength of steel bar.

Key Words
reinforced concrete columns; distributed–steel Bar; finite element method; axial loads; seismic effects

Address
Mao Ye, Yinpei Pi and Min Ren : Guangzhou University – Tamkang University Joint Research Center for Engineering Structure Disaster, Prevention and Control, Guangzhou University, 230 Wai Huan Xi Road, GuangZhou Higher education Mega Center, GuangZhou, Guangdong Province, PR China

Abstract
We present a semi-rigid connection estimation method by using cross modal strain energy method. While rigid or pinned assumptions are adopted for steel frames in traditional modeling via finite element method, the actual behavior of the connections is usually neither. Semi-rigid joints enable connections to be modeled as partially restrained, which improves the quality of the model. To identify the connection stiffness and update the FE model, a newly-developed cross modal strain energy (CMSE) method is extended to incorporate the connection stiffness estimation. Meanwhile, the relations between the correction coefficients for the CMSE method are derived, which enables less modal information to be used in the estimation procedure. To illustrate the capability of the proposed parameter estimation algorithm, a four-story frame structure is demonstrated in the numerical studies. Several cases, including Semi-rigid joint(s) on single connection and on multi-connections, without and with measurement noise, are investigated. Numerical results indicate that an excellent updating is achievable and the connection stiffness can be estimated by CMSE method.

Key Words
finite-element model; model updating; semi-rigid joints; modal frequency; mode shapes

Address
Shuqing Wang, Min Zhang and Fushun Liu : College of Engineering, Ocean University of China, Qingdao, 266100, China

Abstract
Bending behaviors of corroded reinforced concrete (RC) beams under repeated loading were investigated experimentally. A total of twenty test specimens, including four non-corrosion and sixteen corrosion reinforced concrete beams, were prepared and tested. A numerical model for flexural and cracking behaviors of the beam under repeated loading was also developed. Effects of steel corrosion on reinforced concrete beams regarding cracking, mid-span deflection, stiffness and bearing capacity of corroded beams were studied. The impact of corrosion on bond strength as the key factor was investigated to develop the computational model of flexural capacity. It was shown from the experimental results that the bond strength between reinforcement and concrete had increased for specimen of low corrosion levels, while this effect was changed when the corrosion level was higher. It was indicated that the bearing capacity of corrosion beam increased even at a corrosion level of about 5%.

Key Words
steel corrosion; concrete beam; repeated loading; cyclic loading; bending

Address
Congqi Fang, Shuai Yang : Department of Civil Engineering, Shanghai Jiaotong University, Shanghai 200240, China
Zhang Zhang : Shanghai Third Harbour Engineering Science & Technology Research Institute CO., LTD, Shanghai 200030, China

Abstract
The seismic performance of reinforced concrete (RC) frame structures with irregularities leading to soft first floor is studied using capacity assessment procedures. The soft first story effect is investigated for the cases: (i) slab-column connections without beams at the first floor, (ii) tall first story height and (iii) pilotis type building (open ground story). The effects of the first floor irregularity on the RC frame structure performance stages at global and local level (limit states) are investigated. Assessment based on the Capacity Spectrum Method (ATC-40) and on the Coefficient Method (FEMA 356) is also examined. Results in terms of failure modes, capacity curves, interstory drifts, ductility requirements and infills behaviour are presented. From the results it can be deduced that the global capacity of the structures is decreased due to the considered first floor morphology irregularities in comparison to the capacities of the regular structure. An increase of the demands for interstory drift is observed at the first floor level due to the considered irregularities while the open ground floor structure (pilotis type) led to even higher values of interstory drift demands at the first story. In the cases of tall first story and slab-column connections without beams softstory mechanisms have also been observed at the first floor. Rotational criteria (EC8-part3) showed that the structure with slab-column connections without beams exhibited the most critical response.

Key Words
limit states; performance levels; seismic assessment; soft story effect; RC frame structures; pilotis type frame

Address
Maria J. Favvata, Maria C. Naoum and Chris G. Karayannis : Department of Civil Engineering, Democritus University of Thrace, Greece

Abstract
This paper summarises the results of an experimental study to investigate the flexural behaviour of reinforced concrete beams strengthened using carbon-fibre reinforced polymer (CFRP) laminate in fourpoint bending. The experimental parameters included are the reinforcing bar ratio ps and preload level. Four bar ratios were selected (ps = 0.13 to 0.86%), representing the section of two longitudinal tensile reinforcements, with diameters of 8, 14, 16, and 20 mm in order to reveal the effect of bar ratio on failure load and failure mode. Eight beams that could be considered \"full-scale\" in size, measuring 200 mm in width, 400 mm in total height and 2300 mm in length, were tested. Three beams were selected with different bar ratios (p1, p2, p3), and considered as control specimens (without ), while three other beams identical to the control beams with the same CFRP laminates ratio and a seventh beam with pmin (the lowest bar ratio) were also used. In the second part of the study, two beams with the bar ratio p2 were preloaded at two levels, 50 and 100% of their ultimate loads, and then repaired. This experimental investigation was consolidated using an analytical model. The experimental and analytical results indicate that the flexional capacity and stiffness of strengthened and repaired beams using CFRP laminate were increased compared to those of control beams, and the behaviour of repaired beams was nearly similar to the undamaged and strengthened beams; unlike the ductility of strengthened beams, which was greatly reduced compared to the control.

Key Words
four-point bending; failure; CFRP-strengthening; repair; preload; reinforced concrete; beam

Address
Mohcene Boukhezar, Mohamed Laid Samai, Hacene Houari : Department of Civil Engineering, Faculty of Technology Sciences, University of Constantine 1, Algeria, Route Ain Bey - 25 000, Constantine 25000, Algeria
Habib Abdelhak Mesbah : L.G.C.G.M., INSA of Rennes, University of Rennes 1, France

Abstract
Metallic annular discs with their outer boundary fully constrained are studied with newly derived semi-analytical solutions for the effects of thickness variations under thermal loading and unloading. The plane stress and axisymmetric assumptions were adopted, and the thickness of the disk depends on the radius hyperbolically with an exponent n. Furthermore, it is assumed that the stress state is two dimensional and temperature is uniform in the domain. The solutions include the elastic, elastic-plastic and plasticcollapse behavior, depending on the values of temperature. The von Mises type yield criterion is adopted in this work. The material properties, Young\'s modulus, yield stress and thermal expansion coefficient, are assumed temperature dependent, while the Poisson\'s ratio is assumed to be temperature independent. It is found that for any n values, if the normalized hole radius a greater than 0.6, the normalized temperature difference between the elastically reversible temperature and plastic collapse temperature is a monotonically decreasing function of inner radius. For small holes, the n values have strong effects on the normalized temperature difference. Furthermore, it is shown that thickness variations may have stronger effects on the strain distributions when temperature-dependent material properties are considered.

Key Words
analytical method; collapse/failure; elasto-plastic; plane stress/strain; yield criterion

Address
Yun-Che Wang : Department of Civil Engineering, National Cheng Kung University, Tainan 70101, Taiwan
Sergei Alexandrov : A. Ishlinskii Institute for Problems in Mechanics, Russian Academy of Sciences, 119526 Moscow,Russia
Sergei Alexandrov and Yeau-Ren Jeng : Department of Mechanical Engineering and Advanced Institute of Manufacturing with High-tech Innovations, National Chung Cheng University, 62102 Chia-Yi, Taiwan

Abstract
Numerical damage assessment of Van train station building consisting of three RC blocks due to 2011 Van Earthquakes by nonlinear dynamic analysis is presented. The structural model is created with rigid-end offsets and plastic hinges for nonlinear analysis. Rigid-end offsets are considered for connection areas and proposed for wall-supported elements. In wall-supported elements, walls take place in a limited part of the columns. Nonlinear dynamic analysis of the building with and without rigid-end offsets is performed by using real earthquake records and results are compared. The results show that rigid-end offsets have significant effects on the seismic behavior of the structures.

Key Words
rigid-end offset; wall-supported elements; plastic hinge; nonlinear time history analysis

Address
Serkan Bekiroglu, Abdurrahman sahin, Baris Sevima and Yusuf Ayvaz : Yildiz Technical University, Department of Civil Engineering, 34220, Istanbul, Turkey

Abstract
This paper describes analytical investigation into a new dual function system including a couple of shear links which are connected in series using chevron bracing capable to correlate its performance with magnitude of earthquakes. In this proposed system, called Chevron Knee-Vertical Link Beam braced system (CK-VLB), the inherent hysteretic damping of vertical link beam placed above chevron bracing is exclusively utilized to dissipate the energy of moderate earthquakes through web plastic shear distortion while the rest of the structural elements are in elastic range. Under strong earthquakes, plastic deformation of VLB will be halted via restraining it by Stopper Device (SD) and further imposed displacement subsequently causes yielding of the knee elements located at the bottom of chevron bracing to significantly increase the energy dissipation capacity level. In this paper first by studying the knee yielding mode, a suitable shape and angle for diagonal-knee bracing is proposed. Then finite elements models are developed. Monotonic and cyclic analyses have been conducted to compare dissipation capacities on three individual models of passive systems (CK-VLB, knee braced system and SPS system) by General-purpose finite element program ABAQUS in which a bilinear kinematic hardening model is incorporated to trace the material nonlinearity. Also quasi-static cyclic loading based on the guidelines presented in ATC-24 has been imposed to different models of CK-VLB with changing of vertical link beam section in order to find prime effectiveness on structural frames. Results show that CK-VLB system exhibits stable behavior and is capable of dissipating a significant amount of energy in two separate levels of lateral forces due to different probable earthquakes.

Key Words
two-stage earthquake resisting system, vertical link beam, knee elements, stopper device

Address
Amir Koorosh Vosooq : Department of Structural Engineering, Faculty of Civil Engineering, Tafresh University, Tafresh, Iran
Seyed Mehdi Zahrai : Center of Excellence for Engineering and Management of Civil Infrastructures, School of Civil Engineering, Faculty of Engineering, The University of Tehran, Iran


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