Advanced Materials Research Vols. 255-260

Abstract: Due to the absence of provision for the load and resistance factors in design codes in China, designers often quote the provisions which are given in criterion or guidance of other countries such as USA. However, the partial safety factors of the load are various in different criterions. Based on the reliability theory, the load and resistance factors for progressive collapse resistance design of building structures were determined in this study. Firstly the simplified format of design expression in the ultimate state was obtained according to the expression in routine structural design. Then the failure probability of a structure during design reference period was taken as the sum of the probability of all incompatible failure events in this period, and the objective reliability index of the structure could be obtained. Finally using trial-and-error procedure and JC method, reliability analysis was performed for structural members to obtain the partial safety factors of load effects and resistance and the coefficient for combination value of load effects in design expression in the ultimate state. In this paper the load and resistance factors for progressive collapse resistance design of reinforced concrete structures subjected to blast was calculated as an example, and the recommendation values were given for the application at last.

Abstract: This paper proposes a new model to calculate anchorage length for the compression anchor. Then the analytic solutions for the effective length and the critical length are derived according to the model. The analysis to the solutions show that the larger the rock mass’s elastic modulus, cohesion and internal friction angle, the smaller the anchorage length. Besides, the larger the load, the greater the anchorage length. However, the poisson’s ratio of rock mass nearly has no influence on the anchorage length. It is most important that the two calculation length show great agreement with present codes or specification.

Abstract: The performance of two types of Chinese screw nails in connections between sheathing and wood frame was assessed using ASTM-F1575-03. Specimens were tested in groups of 10, and both parallel-to-grain and perpendicular-to-grain specimens were tested in the case of ASTM-F1676-03. It was found that the type of nail had little effect on the performance of nail joints. Finally a modified model suitable to domestic nails in two directions was established on the basis of Foschi’s exponential model. The model provides useful data on the performance of sheathing-to-lumber connections.

Abstract: In order to study the relationship between strains and corrosion levels of prestressed concrete beams uder fatigue loading, accelerated corrosion method is used to make various corrosion rates of prestressed steel strands. The beams have the same designs and submitted to the same maximum and minimum load during the test. With the corrosion level as main parameter, strains at different position of the beams, such as non-prestressed steel strain, concrete strain in compressive region at mid-span and prestressed steel strain are studied. The test results show that beams with different corrosion rates have the same “three-stage“ law on the development of non-prestressed steel maximum and residual strain,as well as concrete strain and prestress strain. The significant increase of concrete strain is generated due to corrosion after concrete cracking.The increase of non-prestressed steel strain is nearly proportional to the growth of corrosion under the same fatigue load. A relationship was found to be a function. It can be obtained the corrosion rate of prestressed steel when the stress of non-prestressed steel strains are measured.

Abstract: Fatigue behaviors of prestressed concrete beams with different corrosion level are investigated in a series of bonded post-tensioned T-beams. The beams have the same designs and submitted to the same maximum and minimum load during the test. Accelerated corrosion method is used to make various corrosion rates of prestressed steel strands. With the corrosion level as main parameter, such as failure mode, fatigue life, mid-span deflection development, stiffness loss, stress expansion, are studied. The test results show that failure mode is changed fracture of non-prestressed steel bar into prestressed steel strand breaking with the increase of corrosion level. Corrosion reduces fatigue life and stiffness of beams, increase deflection and stress range of non-prestressed steel bar.

Abstract: Detection of crack width is crucial in structural health monitoring of concrete bridge. In this paper, the smart film has been employed to monitor the crack initiation and development in concrete bridges. Under plane stress and two dimension conditions, through structure mechanics behavior analysis, the calculation model for crack width of smart film was constructed based on the shear-lag theory. Calculation model study demonstrated the relationship between crack width and diameter of the smart film, and the crack width could be calculated.

Abstract: One large-diameter and non-circular steel tube was adopted in Henan TV tower (China). This special cross-section consists of three flat plates welded to three arc plates one by one. This paper studies the critical local buckling behavior of steel plates by using the finite element analysis method. Initial geometric imperfections and residual stresses presented in steel plates, material yielding and strain hardening were taken into account in the nonlinear analysis. An experimental study was performed to verify the capacity ability of this special steel tube. Based on the results obtained from the nonlinear finite element analyses and experiments, a set of design recommendations are provided for ensuring the safety of this special tube in Henan TV tower.

Abstract: This paper explores the issue how to improve utilization ratio of CFRP strengthening steel structure in allusion to the diseconomy of steel structure strengthened with CFRP. An experiment including six single axisymmetric steel beams was carried out to study ultimate capacity of single axisymmetric steel beam strengthened with CFRP sheets. These samples were divided into three groups, and each group included two samples strengthened with one and two layers of CFRP sheets respectively. The experimental results show that single axisymmetric steel beam strengthened with CFRP is advantageous over biaxial symmetrical steel beam because the former has superior material utilization ratio. On the basis of the experimental results, a simplified analytical model is put forward for prediction of capacity and material utilization ratio. In the proposed approach, ultimate capacity formula is established and an index named material utilization ratio is suggested to study how to enhance CFRP utilization ratio. The analytical calculation results state clearly that steel beam strengthened with enough CFRP is favorable in improving capacity and material utilization and owns optimal utilization ratio. Above all, the proposed approach is convenient and accurate enough for practical application in material utilization assessmetn and capacity design.

Abstract: Finite element analysis (FEA) method is used to study the mechanical properties of headed studs for composite truss joint. The results show that the shear forces in the first few rows of headed studs are much greater than others. The shear forces in the rear headed studs decrease gradually. This study shows that the stiffness of headed studs, the layout of headed studs, and the steel backing plate are the main influencing factors on shear forces of headed studs. It is also expected that the results presented in this paper would be useful as references for the further research and the design of composite truss bridge and composite joint.

Abstract: The static failure can be seen as a special fatigue failure, which means the static failure is the fatigue failure only bearing one cycle under the ultimate-strength loading. By learning from the analysis of fatigue damage, the stress- strain curve and damage of steel fiber reinforced concrete under uniaxial loading have been studied in this paper. The damage evolution equation can be derived from the damage theory, and it can be used to describe the relationship between the damage variable and strain. According to the strain equivalence principle, the corresponding constitutive equation considering damage can be obtained. Finally, comparisons among test results, the model and ansys simulation results show that the model is suitable to describe the uniaxial stress-strain curves of steel fiber reinforced concrete.