Key Engineering Materials Vols. 400-402

Abstract: This paper presents experimental results of cyclic loading tests carried out on three L-shaped prestressed concrete beam-column corner joints. Three types of reinforcing methods to enhance the anchorage performance of beam and column longitudinal reinforcing bars were studied based on the experimental results such as the load-displacement relation curves, deformation capacity, prestressing force variation, and strain measurements of the beam and column reinforcing bars. The test specimens were KPCL1 with the column longitudinal reinforcement with 180-degree hooks at their ends, KPCL2 with the column longitudinal reinforcement bent in a U-shape, and KPCL3 with U-shaped column longitudinal reinforcement and additional transverse reinforcement on the beam longitudinal reinforcement. It can be concluded that the anchorage performance was somehow enhanced by the three reinforcing methods in the positive direction of loading (closing direction), while in the negative direction of loading (opening direction) there was no remarkable improvement.

Abstract: An experimental investigation was undertaken into the seismic performance of a precast prestressed concrete frame system. A total of three beam-to-column connection models were designed, built, and tested to failure to evaluate their strength and ductility properties under cyclic loading. The comparative study showed that the hysteretic loops were full and the joints had better energy dissipation capacity. It was concluded that satisfactory seismic performance could be expected from this frame system if the slip of the U-shaped reinforcing steel bar was controlled well on the zone of joint. Then the finite element method (FEM) was used to analyze the specimen and the calculation results were in good agreement with those of the test.

Abstract: Based on the principle of restrained concrete, this paper presents a new-type concrete filled steel tubular column-slab joint. This new-type joint is characterized by keeping the concrete floor slab continuous while breaking the steel tube of the column for the joint, thus joining the slab and the concrete filled steel tubular(CFST) columns at the top and the bottom of the slab. The joint has the advantage of transferring loads dependably, constructing conveniently and saving on the cost. Three groups of experiments (21 specimens contained) were performed to test the safety of the joint and investigate its axial bearing capacity. The results show that the joint is dependable and feasible in engineering applications. In addition, this paper studies the working mechanism and mechanical properties of the joint under axial compression, discusses the factors to influence its axial bearing capacity, and finally brings out the formula of the joint’s bearing capacity under axial compression that adapts to engineering applications, which conservatively evaluate the result of the experiments.

Abstract: Integrated simple and complete model similarity theory of this structure are set up in this paper. Selection about model reinforced concrete block masonry materials is presented when simple similar model is adopted in testing. Correlations between model and prototype results in basic strength characteristics of masonry prism are reported based on theory analysis. This includes axial compression, joint shear for ungrouted prisms and grouted prisms. The model testing indicated that the structure adopting simple similarity model can accord with the prototype masonry prisms results. The monotonic shear testing of two-story model reinforced masonry shear wall in different compressive forces was performed. The testing results showed that the model structure can accord with the prototype masonry walls results. The shear bearing capacity of model structure is 0.94 times than that of prototype structure without axial compressive force. The shear bearing capacity of model wall is 1.08 times larger than that of prototype wall when the axial stress equal to 1.5 .Model testing and theory foundation adopting simple similar model is erected to carry out reinforced masonry structure.

Abstract: Based on 3D strut-and-tie analogy developed for analyzing the load-transferring mechanism of deep pile cap, this paper focuses on the effect of different longitudinal reinforcement layouts at the lower part of cap on the mechanical behaviors of deep four-pile cap. Besides a common layout of uniformly distributed reinforcement by the flexural theory, three different layouts of concentrated reinforcement over piles were designed by 3D strut-and-tie analogy. All specimens were limited in same reinforcement percentages, dimensions, materials and test procedures. Four specimens with the scale ratio of 1/5 were tested under the statically incremental gravity loading. The load capacity, deflection, strain of longitudinal reinforcement of specimens were measured, and the failure mode, crack propagation, deformation of specimens and stress distribution of reinforcement were analyzed. Through comparisons of the test results among all specimens, it was found that deep pile cap failed in shear and corner-pile punching whether with concentrated or uniform reinforcement, and the reinforcement concentrated over each two adjacent piles, similar to the tension bars in the strut-and-tie model, had considerable advantages than common uniform reinforcement layout. The ultimate strength of deep pile cap with concentrated reinforcement was significantly increased, while the improvement of deformation resistance and brittleness of deep pile cap was limited. According to above findings, the appropriate reinforcement layouts for deep pile cap were suggested in this paper.

Abstract: According to the definition about the positive and negative gradient temperature distribution of structural cross section in the Chinese bridge design specification of General Code for Design of Highway Bridge and Culverts (JTG D60-2004), same temperature loads are applied to beam model and solid model of a typical there-span prestressed concrete continuous box-girder bridge to compare the numerical results of thermal stresses calculated from the two finite element models. The beam model is built through professional software Doctor Bridge that is prevailing in China for structural static analysis of bridge design, while the solid model is built using ANSYS. Between the two models, the numerical results of total thermal stress regarded to be added up with self-restrained stress and secondary stress are compared. The results from solid model are found to be much more conservative than from element model. The identity and diversity of the two series of results and the reasons for the generation of the diversity are expounded. It is recommended that the thermal stress calculated from solid model be better to be taken into account in a design so as to examine or amend the results that calculated through the professional software based on bar system FEM theory.

Abstract: Rapid moisture loss in concrete and the coupled shrinkage strain in concrete elements cause distress in structural members at early ages. The shrinkage stresses and the associated cracks can be reduced by controlling the rate of the moisture loss. However, under some circumstances, controlling the rate of the moisture rate is not practically possible which may add additional cost to the concrete construction. A finite element based technique is suggested in this paper to predict the shrinkage stresses and consequently predict the possibility of having shrinkage cracks. The technique utilizes the analog between the heat transfer and moisture diffusion, thermal stresses and shrinkage stresses. The analysis was performed using thermal and structural modules in the commercial finite element software ANSYS. The process described in this work makes the determination of restrained shrinkage stresses in problems of concrete structures readily accessible to design, repair and construction engineers.

Abstract: Heliostat is the key part of Solar Tower power station, which requires extremely high accuracy in use. But it’s sensitive to gust because of its light structure, so effect of wind load should be taken into account in design. Since structure of heliostat is unusual and different from common ones, experimental investigation on rigid heliostat model using technology of surface pressure mensuration to test 3-dimensional wind loads in wind tunnel was conducted. The paper illustrates distribution and characteristics of reflector’s mean and fluctuating wind pressure while wind direction angle varied from 0° to 180° and vertical angle varied from 0° to 90°. Moreover, a finite element model was constructed to perform calculation on wind-induced dynamic response. The results show that the wind load power spectral change rulers are influenced by longitudinal wind turbulence and vortex and are related with Strouhal number; the fluctuating wind pressures between face and back mainly appear positive correlation, and the correlation coefficients at longitudinal wind direction are smaller than those at lateral direction; the fluctuating wind pressures preferably agree with Gaussian distribution at smaller vertical angle and wind direction angle. The wind-induced response and its spectrums reveal that: when vertical angle is small, the background responsive values of reflector’s different parts are approximately similar; in addition, multi-phased resonant response occurring at the bottom. With the increase of , airflow separates at the near side and reunites at the other, as produces vortex which enhances dynamic response at the upper part.

Abstract: A set of formulae to calculate short-term behavior of simply supported prestressed concrete box girders under dead load and prestress are established based on energy method, in which shear lag and effect of prestressed steel and non-prestressed steel are taken into account. As the time-dependent relationship between stress and strain of concrete, equilibrium of sectional forces and compatibility equation are introduced, a novel approach to analyze long-term behavior of prestressed concrete box girders is presented, and the theoretical formulae considering the synthetic effect of creep and shrinkage of concrete, relaxation of prestressed steel, shear lag and restriction of steels are deduced, which can be used directly to calculate time-dependent deflection of box girder, stresses and strains of concrete and steel at any location at any time. Comparison of theoretical values shows that that the long-term deflection increases by shear lag while distribution of transverse concrete stresses become even by concrete creep and shrinkage.

Abstract: Approach slabs are commonly used to provide a smooth transition between the roadway and the highway bridge. Conventional construction of approach slabs uses cast-in-place reinforced concrete slabs that are anchored to the abutment. Maintenance of bridges, however, often requires repair or replacement of approach slabs due to damage from traffic, washout of fill materials, and settlement of the approach embankment etc. This paper describes recent tests of full-size approach slabs with conventional steel reinforcement as well as pultruded fiber-reinforced polymer grating and glass fiber- reinforced polymer rebars.