Key Engineering Materials Vols. 400-402

Abstract: This paper presents the field measurement results of wind effects on the world’s tallest reinforced concrete building (CITIC Plaza, 391 m high) located in Guangzhou during the passage of typhoon Pabuk on August 10, 2007. The field data such as wind speed, wind direction and acceleration responses were simultaneously and continuously recorded from the tall building by a remote monitoring system. Detailed analysis of the field data was carried out to investigate the wind effects on the super tall building. The characteristics of the typhoon-generated wind including turbulence intensity, gust factor, turbulence integral length scale and power spectral density of fluctuating wind speed were analyzed. The dynamic characteristics of the buildings were determined from the field measurements and comparison with those calculated from the computational model of the building was made. The measured natural frequencies of the two fundamental sway modes of the building were found to be larger than those calculated. The damping ratios of the building were evaluated by random decrement technique, which demonstrated obvious amplitude-dependent characteristics and increased with increasing amplitude of the building during Typhoon Pabuk.

Abstract: the soil-structure appeared slipped of roadway under earthquake, using the Coulomb contact surface model and built soil-structure of roadway contact model for analyzing, and got slip rule at different direction and position under horizontal and vertical direction and pointed out the corner as the weakness position; the beneath of roadway has more slipping; the vault is vulnerable to the level of shear failure; and gave reference for roadway structure for the seismic design.

Abstract: 81 concrete prism specimens under axial compression were tested to invesgigate the size effect on the axial load stength. Three different kinds of specimens with the dimension 100×100×300mm, 150×150×300mm, 200×200×400mm were tested. The parameters including compressive strength of concrete and aggregate composition are taken into consideration. Three different strength grades of concrete and three different aggregate composition are included in those specimens. The test method are undertaken according to ASTM C 39/C 39M-2005. Based on the test results, a new size effect law for different kinds of concrete in prismatical compressive strength is suggested and those relative parameters on the size effect are discussed.

Abstract: An experimental investigation is reported into the size effect for compressive strength from 36 concrete prism specimens under axial loading and with three different kinds of dimensions of 100×100×300mm, 150×150×300mm, 200×200×400mm. Such parameters as strength grade of concrete and reinforcement ratio are taken into consideration. Three different strength grades of concrete and two different reinforcement ratio are included in those specimens, all tests are undertaken according to ASTM C 39/C 39M-2005. Based on the results obtained, a new size effect law for different kinds of concrete in prismatical compressive strength is suggested and those relative parameters on the size effect are discussed.

Abstract: For continuous composite beams that in normal working stage, due to concrete cracks at negative moment region are restricted by transverse tendon reinforcements at the slab, it would be reasonable to consider concrete contribution to the bending capacity of such composite beams. Based on this, a variable stiffness method is proposed in this paper to calculate the composite beam deflection. Before concrete slab cracks, the flexural stiffness (the maximum value) is calculated according to the reduced transformed beam section, with the consideration of concrete contribution; After concrete cracks, this stiffness value will be decreased as per the increase of the concrete crack, and at final stage, when concrete contribution to the flexural stiffness reach zero, the stiffness value reach it’s minimum value. The loads capacity at such maximum and minimum stiffness values could be considered as the beam capacity before concrete cracking as per current code, and the elastic moment capacity after concrete cracking respectively, while the stiffness between these maximum and minimum values could be determined by linear interpolation. The bending stiffness derived from this method has a higher precision than the method presented in current China specification in which the concrete contribution is totally neglected. Especially, this procedure would be more useful for those prestressed concrete composite beams, as they have higher crack- resistance capability.

Abstract: An energy absorbing stiff test facility has been developed for obtaining stable and controlled shear failure of reinforced concrete beams. Using two hydraulic jack and a cross steel beam to act as the stiffener and energy absorbing elements, test facility allows the monitoring of the complete curve of load versus mid-span deflection (including the post-peak region) of shear critical beams. To prove the feasibility of this test facility, the stiff test facility was measured when test facility were loaded up and down. Then, the shear failure experiments of 4 full size reinforced concrete beams were processed. The results indicate that the post-peak branch of the load versus mid-span deflection of the shear-critical reinforced concrete beams without web reinforcement was steeper than that of beams with web reinforcement and hence the stiff test facility was more stable for beams with web reinforcement.

Abstract: 19 RC beams with shear span-to-depth equal to 3 were tested under a stiff testing facility, and complete load-deflection curves including the post-peak branch were obtained. Based on the test results the effects of concrete strength, stirrups strength, inclined stirrup angle, the amount of longitudinal reinforcement on failure mode, shear ductility index and shear capacity were analyzed. The test results were compared with the shear design approaches of Chinese Code and American Code. The results indicate that the shear failure of beam with appropriate web reinforcement has finite ductility. High-strength concrete beams with high-strength stirrups can increase not only the shear capacity, but also the shear ductility. The shear capacity of beams with high-strength concrete and stirrup can be designed with Chinese Code, but shear capacity of high-strength concrete beams without stirrups, or with the smaller amount of longitudinal reinforcement, and normal strength concrete beams with high-strength stirrups may be over-estimated by the Code.

Abstract: A precast, prestressed concrete girder with circular web openings allows building service systems (mechanical, electrical, communications, and plumbing) to cross the girder line within the member’s depth, reducing a building’s floor-to-floor height and the overall height of the structure. These height reductions have the potential to improve the competitiveness of total precast concrete structures versus other types of building systems. The experimental program reported in this paper tested five full-scale inverted-tee girders with circular web openings to failure, to evaluate the openings’ effect on girder behavior. The girders failed in a ductile manner due to diagonal cracking above the openings. The tested girders were designed using available recommendations in the existing literatures. It was observed that concrete fractured from tension zones around an opening, with cracks developing vetically towards the beam flanges. A beam would collapse when the cracks reached the flanges. In the present work, an analytical solution is developed for the load-deflection calculation of prestressed beam with web openings at any load stage. The solution assumes a trilinear deflection response characterized by the flexural cracking initiation, steel yielding, and ultimate capacity. Closed form expressions are presented for the case of simple beams subjected to four-points loading. These expressions are modified from present ACI code equations by incorporating appropriate laboratory determined coefficients in order to predict more precisely with some degree of conservativeness on flexural load-point deflection with any extent of uncracked, postcracked, and postyielded region along their spans. Accordingly, a simplified analysis procedure is developed by adopting a trilinear load-deflection response. The effectiveness of the simplified procedure is demonstrated by comparing its results to those of the analytical solution and the experimental values.

Abstract: During earthquake, the inelastic action in the plastic hinge regions of structures and bridges results in significant reversed deformation and failure of the critical components because of cumulative damage. To simulate seismic behavior of structure members and develop a simplicity damage criterion for circular concrete filled steel tubular (CFT) columns subjected to a series of earthquake excitations, an experimental study was undertaken to investigate the cumulative damage and relationship between low cycle fatigue life and displacement amplitude. Two types of large scale circular CFT columns with different kinds of seam weld and inner concrete compressive strength including nine specimens were tested under quasi static loading with constant and variable cyclic amplitudes. The test data were evaluated with the fatigue model relating deformation and fatigue life. Fatigue life expressions for application in damage-based seismic design are developed.

Abstract: Eight weak reinforced concrete beam-column connections and two strong ones subjected to cyclic loads were tested. Effects of the one-way slab, top reinforcement ratio of the beam as well as the transverse reinforcement ratio inside the joint on the seismic behavior of reinforced concrete beam-column connections were primarily investigated. Tests results show that, when subjected to the negative moment, the beam flexural resistance increases notably due to the presence of the slab. However, failure mode of the weak connection transforms from the beam flexural failure to the joint shear failure, resulting from the increased joint shear brought by the slab participation. Besides, the presence of the slab reduces the ultimate relative rotation, ductility and energy-dissipation capacity of the connection. Generally, weak connections can receive more benefit from the one-way slab than strong connections. Connections with less amount of top reinforcement in the beam exhibit better ductility and energy-dissipation capacity, which indicates that it is not always good to strengthen the beam negative moment zones in existing structures. The transverse reinforcement inside the joint has little effect on the seismic behavior of the weak connection with a one-way slab.