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Volume 27, Number 6, June25 2018

Seismic excitations may impart a significant amount of energy into structures. Modern structural design attitudes tend to absorb some part of this energy through special dissipaters instead of heavy plastic deformations on the structural members. Different types of dissipater have been generated and utilized in various types of structures in last few decades. The expected earthquake damage is mainly concentrated on these devices and they may be replaced after earthquakes. In this study, a low-cost device called energy dissipative steel cushion (EDSC) made of flat mild steel was developed and tested in the Structural and Earthquake Engineering Laboratory (STEELab) of Istanbul Technical University (ITU). The monotonic and cyclic tests of EDSC were performed in transversal and longitudinal directions discretely. Very large deformation capability and stable hysteretic behavior are some response properties observed from the tests. Load vs. displacement relations, hysteretic energy dissipation properties as well as the closed form equations to predict the behavior parameters are presented in this paper.

Key Words
steel cushion; dissipation; energy dissipater; fuse element; hysteretic energy

(1) Hasan Ozkaynak:
Beykent University, Department of Civil Engineering, Maslak, Istanbul, Turkey;
(2) Arastoo Khajehdehi, Ahmet Gullu, Faraz Azizisales:
Istanbul Technical University, Institute for Science and Technology, Maslak, Istanbul, Turkey;
(3) Ercan Yuksel:
Istanbul Technical University, Faculty of Civil Engineering, 34469, Maslak, Istanbul, Turkey;
(4) Faruk Karadogan:
Isik University, Department of Civil Engineering, Sile, Istanbul, Turkey.

Buckling-restrained braces (BRBs) have received considerable attention in seismic design of various types of structures. Conventional BRBs are composed of steel core and surrounding steel tube filled with concrete. Eliminating the steel tube can be advantageous to BRB. In this study the idea of replacing the steel tube by CFRP layers in BRBs is proposed. The advantages of this type of BRB are mentioned, and its design criteria are introduced. The construction procedure of two BRB specimens is described. The specimens are uniaxially tested based on moderate, and severe earthquake levels and the performance of the specimens is investigated. The backbone curves resulted from the hysteresis curve are presented for the design proposes. The results of this study show that CFRP layers can effectively provide the expected performance of the encasing, and the proposed BRB can be considered a viable alternative to the conventional BRBs.

Key Words
buckling-restrained brace; CFRp layers; cyclic test; design criteria

Faculty of Civil Engineering, University of Tehran, Tehran, Iran.

This paper presents experimental and analytical results of fiber reinforced polymer (FRP) confined steel tubular columns under transverse impact loads. Influences of applied impact energy, thickness of FRP jacket and impact position were discussed in detail, and then the impact responses of FRP confined steel tubes were compared with bare steel tubes. The test results revealed that the FRP jacket contributes to prevent outward buckling deformation of steel at the clamped end and inward buckling of steel at the impact position. For the given applied impact energy, specimens wrapped with one layer and three layers of FRP have the lower peak impact loads than those of the bare steel tubes, whereas specimens wrapped with five layers of FRP exhibit the higher peak impact loads. All the FRP confined steel tubular specimens displayed a longer duration time than the bare steel tubes under the same magnitude of impact energy, and the specimen wrapped with one layer of FRP had the longest duration time. In addition, increasing the applied impact energy leads to the increase of peak impact load and duration time, whereas increasing the distance of impact position from the clamped end results in the decrease of peak impact load and the increase of duration time. The dynamic analysis software Abaqus Explicit was used to simulate the mechanical behavior of FRP confined steel tubular columns, and the numerical results agreed well with the test data. Analytical solution for lateral displacement of an equivalent cantilever beam model subjected to impact load was derived out. Comparison of analytical and experimental results shows that the maximum displacement can be precisely predicted by the present theoretical model.

Key Words
FRP; steel tubes; dynamic response; transverse impact; vibration theory

College of Civil Engineering, Nanjing Tech University, Nanjing 211816, People's Republic of China.

In this study, the different energy demands in reinforced concrete (RC) wall piers, coupled by buckling restrained braces (BRBs), are investigated. As well as this, a single plastic hinge approach (SPH) and an extended plastic hinge (EPH) approach is considered for the wall piers. In the SPH approach, plasticity can extend only in the 0.1H adjacent to the wall base while, in the EPH approach, the plasticity can extend anywhere in the wall. The seismic behavior of 10-, 20- and 30-storey structures, subjected to near-fault (NF) as well as far-fault (FF) earthquakes, is studied with respect to the energy concepts involved in each storey. Different kinds of energy, including inelastic, damping, kinetic, elastic and total input energy demand, are investigated. The energy contribution from the wall piers, as well as the BRBs in each model, are studied. On average, for EPH approach, the inelastic demand portion pertaining to the BRBs for NF and FF records, is more than 60 and 80%, respectively. In the SPH approach, these ratios are 77 and 90% for the NF and FF events, respectively. It appears that utilizing the BRBs as energy dissipation members between two wall piers is an efficient concept.

Key Words
energy demand; reinforced concrete wall; buckling restrained braces; near-fault

Department of Civil Engineering, Mahdishahr Branch, Islamic Azad University, Mahdishahr, Iran.

One of the most important design criteria in military tunnels and armoured doors is to resist the blast loads with minimum structural weight. This can be achieved by using steel sandwich panels. In this paper, the nonlinear behaviour of steel sandwich panels, with different core materials: (1) Hollow (no core material); (2) Rigid Polyurethane Foam (RPF); and (3) Vulcanized Rubber (VR) under free air blast loads, was investigated using detailed 3D nonlinear finite element models in Ansys Autodyn. The accuracy of the finite element model proposed was verified using available experimental test data of a similar steel sandwich panel tested. The results show the developed finite element model can be reliably used to simulate the nonlinear behaviour of the steel sandwich panels under free air blast loads. The verified finite element model was used to examine the different parameters of the steel sandwich panel with different core materials. The result shows that the sandwich panel with RPF core material is more efficient than the VR sandwich panel followed by the Hollow sandwich panels. The average maximum displacement of RPF sandwich panel under different ranges of TNT charge (1 kg to 10 kg at a standoff distance of 1 m) is 49% and 53% less than the VR and Hollow sandwich panels, respectively. Detailed empirical design equations were provided to quantify the maximum deformation of the steel sandwich panels with different core materials and core thickness under a different range of blast loads. The developed equations can be used as a guide for engineer to design steel sandwich panels with RPF and VR core material under a different range of free air blast loads.

Key Words
3D nonlinear finite element analysis; rigid polyurethane foam (RPF); vulcanized rubber (VR); free air blast loads

(1) T.Y. Yang:
International Joint Research Laboratory of Earthquake Engineering, Tongji University, Shanghai, China;
(2) T.Y. Yang, Mohamed Rashad:
Department of Civil Engineering, University of British Columbia, Vancouver, Canada.

The design criteria and the corresponding performance levels characterize the response of extended stiffened end-plate beam-to-column joints. In order to guarantee a ductile behavior, hierarchy criteria should be adopted to enforce the plastic deformations in the ductile components of the joint. However, the effectiveness of thesecriteria can be impaired if the actual resistance of the end-plate material largely differs from the design value due to the potential activation of brittle failure modes of the bolt rows (e.g., occurrence of failure mode 3 in the place of mode 1 per bolt row). Also the number and the position of bolt rows directly affect the joint response. The presence of a bolt row in the center of the connection does not improve the strength of the joint under both gravity, wind and seismic loading, but it can modify the damage pattern of ductile connections, reducing the gap opening between the end-plate and the column face. On the other hand, the presence of a central bolt row can influence the capacity of the joint to resist the catenary actions developing under a column loss scenario, thus improving the joint robustness. Aiming at investigating the influence of these features on both the cyclic behavior and the response under column loss, a wide range of finite element analyses (FEAs) were performed and the main results are described and discussed in this paper.

Key Words
steel bolted joints; seismic design; column loss; robustness; moment-rotation response; cyclic behavior

Department of Structures for Engineering and Architecture, University of Naples \"Federico II\", Via Forno Vecchio 36, 80134 Naples, Italy.

This study proposed a new type of concrete column that was confined with both steel angles and spiral hoops, named angle-steel and spiral confined concrete (ASCC) column. A total of 22 ASCC stub columns were tested under axial compression to investigate their behavior. For a comparison, three angle-steel reinforced concrete (ARC) stub columns were also tested. The test results indicated that ASCC column had a superior mechanical performance. The strength, ductility and energy absorption were considerably increased due to the improvement of confinement from spiral hoops. The confinement behavior and failure mechanism of ASCC column were investigated by the analysis of failure mode, load-deformation curve and sectionstrain distribution. Parametric studies were carried out to examine the influences of different parameters on the axial compression behavior of ASCC columns. A calculation approach was developed to predict the ultimate load carrying capacity of ASCC columns under axial compression. It was validated that the predicted results were in well agreement with the experimental results.

Key Words
ASCC column; axial compression; confinement; spiral; ultimate load carrying capacity; toughness

(1) Chunheng Zhou, Zongping Chen:
College of Civil Engineering and Architecture, Guangxi University, 100 Daxue road, Nanning, China;
(2) Zongping Chen:
Key Laboratory of Disaster Prevention and Structure Safety of Chinese Ministry of Education, 100 Daxue road, Nanning, China;
(3) Sheldon Q. Shi, Liping Cai:
Department of Mechanical and Energy Engineering, University of North Texas, 3940 N. Elm – F101 P Denton, Texas, USA;
(4) Sheldon Q. Shi:
School of Resources, Environment, and Materials, Guangxi University, Nanningi, China.

In the present work, the recently developed non-polynomial shear deformation theories are assessed for thermo-mechanical response characteristics of laminated composite plates. The applicability and accuracy of these theories for static, buckling and free vibration responses were ascertained in the recent past by several authors. However, the assessment of these theories for thermo-mechanical analysis of the laminated composite structures is still to be ascertained. The response characteristics are investigated in linear and non-linear thermal gradient and also in the presence and absence of mechanical transverse loads. The laminated composite plates are modelled using recently developed six shear deformation theories involving different shear strain functions. The principle of virtual work is used to develop the governing system of equations. The Navier type closed form solution is adopted to yield the exact solution of the developed equation for simply supported cross ply laminated plates. The thermo-mechanical response characteristics due to these six different theories are obtained and compared with the existing results.

Key Words
thermo-mechanical analysis; shear deformation theory; Navier solution; laminated plate

(1) Yadwinder S. Joshan, Neeraj Grover:
Department of Mechanical Engineering, Thapar Institute of Engineering and Technology, Patiala 147004, Punjab, India;
(2) B.N. Si:
Department of Aerospace Engineering, Indian Institute of Technology Kharagpur, 721302, West Bengal, India.

investigation on the thermal buckling resistance of simply supported FGM beams having parabolic-concave thickness variation and temperature dependent material properties is presented in this paper. An analytical formulation based on the first order beam theory is derived and the governing differential equation of thermal stability is solved numerically using finite difference method. a function of thickness variation is introduced which controls the parabolic variation intensity of the beam thickness without changing its original material volume. The results showed the high importance of taking into account the temperature-dependent material properties in the thermal buckling analysis of such critical beam sections. Different Influencing parametric on the thermal stability are studied which may help in design guidelines of such complex structures.

Key Words
FGM beam; thermal buckling; stability analysis; finite difference method; parabolic-concave; thickness variation

(1) Othman Arioui:
Department of Civil Engineering, University of Oran of Science and Technology, Oran, Algeria;
(2) Othman Arioui:
Laboratory of Structural Mechanics and Structural Stability, University of Oran of Science and Technology, Oran, Algeria;
(3) Khalil Belakhdar:
Department of Science and Technology, University Centre of Tamanrasset, BP 10034 Sersouf, Tamanrasset, Algeria;
(4) Abdelhakim Kaci:
Department of Civil Engineering and Hydraulics, University of Saida, Algeria;
(5) Khalil Belakhdar, Abdelhakim Kaci, Abdelouahed Tounsi:
Laboratory of Materials and Hydrology, University of Sidi Bel Abbes, Algeria;
(6) Abdelouahed Tounsi:
Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia.

weak-form formulation of finite annular prism methods (FAPM) based on Reissner's mixed variational theorem (RMVT), is developed for the quasi three-dimensional (3D) static analysis of two-directional functionally graded (FG) circular plates with various boundary conditions and under mechanical loads. The material properties of the circular plate are assumed to obey either a two-directional power-law distribution of the volume fractions of the constituents through the radial-thickness surface or an exponential function distribution varying doubly exponentially through it. These FAPM solutions of the loaded FG circular plates with both simply-supported and clamped edges are in excellent agreement with the solutions obtained using the 3D analytical approach and two-dimensional advanced plate theories available in the literature.

Key Words
circular plates; finite annular prism methods; functionally graded material; Reissner's mixed variational theorem; rule of mixtures; various boundary conditions

Department of Civil Engineering, National Cheng Kung University, Taiwan, ROC.

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