CIVIL ENGINEERING

This paper adopted an innovative external prestressing method to study the deformation of reinforced concrete T-beams strengthened externally with CFRP tendons through static experiment. Experiments and analytical analysis were conducted to study the influences of concrete strength, reinforcement ratio of the non-prestressed tensile steel bars and tension control stress of the CFRP tendons on the performance of the reinforced T-beams. The results shown that: (1) The deflections of the T-beams were reduced significantly compared with the non-strengthened beam, especially after cracking; (2) In comparison with concrete strength, steel reinforcement ratio of the T-beam and the tension control stress of the CFRP tendons have greater effects on the deflection of the beam. On the basis of the above observations and the available Chinese design codes for prestressed concrete structures, a modified formula of short-term bending rigidity was proposed, in which the cracking stiffness reduction factor β cr was amended and two new design parameters, i.e. the ratio of prestressing strength λ and CFRP tendon's strain reduction ATINER CONFERENCE PAPER SERIES No: CIV2013-0645 7 coefficient Ω were introduced. The modified formula was then validated against designs from the design codes. It was found that the deflections predicted by the proposed formula were more accurate, and resulted in safer designs. The new formula has potential to be adopted in practical designs.

Abstract： ： ： ：The concrete simple supported beams were strengthened by an innovative device mainly includes oblique screws and linear CFRP tendons. A static experimental study and finite element analysis were conducted to research the flexural capacity and stress changes of CFRP tendons of strengthened beams, and the contrastive analysis was explored between finite element calculation results and test results. The results indicate that the strengthen system can significantly improve the flexural capacity of concrete beams, there is basically a linear relationship between the stress increment of CFRP tendon and the deflection of midspan section, and the finite element calculation value is in agreement with the test results. Based on this, the stress of concrete near holes was analysed using finite element method(FEM), which can provide a reference for practical engineering application.

Addition of fibers into cementitious composites has raised concern over decades, which enables considerable improvement in mechanical and dynamic properties of reinforced concrete (RC) members. In this paper, we present an experimental study on the seismic performance of steel-polypropylene hybrid fiber reinforced concrete (HFRC) columns, which is of vital signifi-cance to postearthquake serviceability of structures. A total of 24 specimens subjected to combined constant axial load and cyclic lateral force were investigated. The main variables involve fiber type, shear span ratio, axial compression ratio, and reinforcement ratio (longitudinal and transverse). The failure modes, ultimate bearing capacity and deformation capacity were analyzed. The experimental results showed that the presence of hybrid fibers in RC columns had positive influence on im-proving the seismic bearing capacity. The improvement ratio could reach to 15%~20% when a relative high axial compression was applied. Moreover, in comparison to RC columns, HFRC columns exhibited a notable synergetic effect in terms of ductility and energy dissipation capacity, particularly for columns with a higher axial compression ratio. Subsequently, on the basis of principles of equilibrium and compatibility, analytical equations to estimate the seismic bending moment capacity and shearing force capacity were developed, which took into account the syn-ergetic effect of hybrid fibers. The analytical solutions were then validated by the test results, and the correlations were observed in reasonable accuracy.

Workplace accidents are of great concern in the construction industry. Most of those accidents are caused by unsafe behavior in the workplace. Many previous studies have analyzed the causes of workers’ unsafe behaviors, but few have investigated workers’ feelings of insecurity from the perspective of systematic psychological theory. This study developed an attitude–behavior–intervention feedback loop mechanism of construction workers and used the dual-attitude theory to explain the occurrence mechanisms of unsafe behavior. Using this mechanism, an active-intervention system-dynamics model and a passive-intervention system-dynamics model were designed and simulated. The coefficient of the system dynamics equation in the simulation model involved meta-analysis to combine the correlation coefficients of existing studies, which increased the sample size and improved the statistical test efficiency. The results show that an implicit safety attitude has a more significant impact on safety...