Current Issue : April - June Volume : 2017 Issue Number : 2 Articles : 6 Articles
The bearing capacities of concrete-filled steel tubes are normally derived through experiments with small-scale specimens, but it\nis uncertain whether such derivations are appropriate for the much larger components used in practical engineering. This study\ntherefore investigates the effect of different diameters (219, 426, 630, and 820 mm) on the axial compression of short concrete\ncolumns in steel (Q235) tubes. It is found that the peak nominal stress decreases with increasing specimen size and that the axial\nbearing capacity is determined by three separate components: the cylinder compressive strength of the concrete, the improvement\nin strength due to the confining effect of the steel tube, and the longitudinal strength of the steel tube. At peak load, increases in the\nspecimen diameter reduce the hoop stresses in the steel tube, thereby reducing the strengthening effect of confinement. Vertical\nstress in the steel tube is increased with diameter; therefore, the axial bearing capacity of the steel tube is directly related to the\nspecimen size. Size effect coefficients for these three aspects of bearing capacity are defined and used to develop a size-dependent\nmodel for predicting the axial bearing capacity of large, concrete-filled steel tubes.The model is then validated against experimental\ndata....
The aimof this paper is to understand the structural behaviour of composite slabs. These composite slabs are made of steel and different\nkinds of concrete.Themethodology used in this paper combines experimental studies with advanced techniques of numerical\nsimulations. In this paper, four types of concrete were used in order to study their different structural strengths in composite slabs.\nThematerials used were three lightweight concretes, a normal concrete, and a cold conformed steel deck which has embossments to\nincrease the adherence between concrete and steel. Furthermore, two lengths of slabswere studied to compare structural behaviours\nbetween short and long slabs. m-k experimental tests were carried out to obtain the flexural behaviour of the composite slabs.\nThese tests provide dimensionless coefficients to compare different sizes of slabs. Nonlinear numerical simulations were performed\nby means of the finite element method (FEM). Four different multilinear isotropic hardening laws were used to simulate the four\nconcretes. Coulomb friction contact was used to model the coefficient of friction between steel and concrete. Finally, a chemical\nbond was included to consider sliding resistance in the contact surface between steel and concrete. Experimental and numerical\nresults are in good agreement; therefore, numerical models can be used to improve and optimize lightweight composite slabs....
An anchorage system is necessary in most reinforced concrete structures for connecting attachments. It is very\nimportant to predict the strength of the anchor to safely maintain the attachments to the structures. However, according to\nexperimental results, the existing design codes are not appropriate for large anchors because they offer prediction equations only\nfor small size anchors with diameters under 50 mm. In this paper, a new prediction model for breakout shear strength is suggested\nfrom experimental results considering the characteristics of large anchors, such as the prying effect and size effect. The proposed\nequations by regression analysis of the derived model equations based on the prying effect and size effect can reasonably be used\nto predict the breakout shear strength of not only ordinary small size anchors but also large size anchors....
Although the efficiency of steel fibres for improving mechanical properties (cracking resistance and failure toughness) of the\nconcrete has been broadly discussed in the literature, the number of studies dedicated to the fibre effect on structural behaviour of\nthe externally bonded elements is limited. This experimental study investigates the influence of steel fibres on the failure character\nof concrete elements strengthened with external carbon fibre reinforced polymer sheets. The elements were subjected to different\nloading conditions. The test data of four ties and eight beams are presented. Different materials were used for the internal bar\nreinforcement: in addition to the conventional steel, high-grade steel and glass fibre reinforced polymer bars were also considered.\nThe experimental results indicated that the fibres, by significantly increasing the cracking resistance, alter the failure character from\nsplitting of the concrete to the bond loss of the external sheets and thus noticeably increase the load bearing capacity of the elements....
The strain rate effect of reinforcing steel bars is generally indispensable for modeling\nthe dynamic responses of reinforced concrete structures in blast and impact events. A systematic\nexperimental investigation was conducted on the strain rate behavior of reinforcing steel bar grades\nHPB235, HRB335, HRB400, and HRB500 which are widely used in the field of civil engineering in\nChina. The dynamic testing was performed using a servo-hydraulic Instron VHS160/100-20 in a\nstrain rate range from 2 to 75 sâË?â??1. Stress-strain curves at preset strain rates were obtained. The test\ndata were then used to derive the parameters in a model based on the dynamic increase factors (DIFs)\nof strengths and the Johnsonââ?¬â??Cook constitutive model. Results indicated that a significant strain rate\neffect was observed for the four rebar grades. The dynamic yield strengths increased from 13% to 41%\nand their ultimate strengths improved from 9% to 19% in the strain rate range during testing. The\nstrain rate behavior of the four rebar grades could be appropriately predicted using the parameters\nin the model based on the DIFs of strengths and the Johnsonââ?¬â??Cook model....
Yonjung Bridge is a hybrid multi span bridge that is designed to transport high-speed trains (HEMU-430X) with maximum\noperating speed of 430 km/h. The bridge consists of simply supported prestressed concrete (PSC) and composite steel girders to\ncarry double railway tracks. The structural health monitoring system (SHM) is designed and installed to investigate and assess the\nperformance of the bridge in terms of acceleration and deformation measurements under different speeds of the passing train. The\nSHM measurements are investigated in both time and frequency domains; in addition, several identification models are examined\nto assess the performance of the bridge.The drawn conclusions show that the maximum deflection and acceleration of the bridge are\nwithin the design limits that are specified by the Korean and European codes.The parameters evaluation of the model identification\ndepicts the quasistatic and dynamic deformations of PSC and steel girders to be different and less correlated when higher speeds\nof the passing trains are considered. Finally, the variation of the frequency content of the dynamic deformations of the girders is\nnegligible when high speeds are considered....
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