Compared with scaled-model testing, full-scale destructive testing is more reliable since the test has no size effect and can truly record the mechanical performance of the structure. However, due to the high cost, only very few full-scale destructive tests have been conducted on the flexural behavior of prestressed concrete (PC) box girders with girders removed from decommissioned bridges. Moreover, related destructive testing on the flexural behavior of a new precast box girder has been rarely reported. To investigate the flexural behavior and optimize the design, destructive testing of a 30-meter full-scale simply supported prestressed box girder was conducted at the construction site. It is illustrated that the failure mode of the tested girder was fracture of the prestressing tendon, and the corresponding maximum compressive strain in the top flange was only 1456 μ ε , which is far less than the ultimate compressive strain (3300 μ ε ). Therefore, the concrete in the top flange was not fully utilized. A nonlinear analysis procedure was performed using the finite strip method (FSM). The validity of the analysis was demonstrated by comparing the analytical results with those of the full-scale test in the field and a scaled model test in a laboratory. Using the developed numerical method, parametric analyses of the ratio of reinforcement were carried out. The prestressing tendon of the tested girder was increased from four strands to six strands in each duct. After the optimization of the prestressed reinforcement, the girder was ductile and the bearing capacity could be increased by 44.3%.
This paper analyzes the existing problems in the practical engineering design, resulting from the mechanical properties of two-way composite concrete slabs with precast ribbed panels (CSPRPs). Due to the influence of the structurally orthotropic characteristic, the calculation formulas for the deflection and bending moments of a CSPRP with three supported edges and one clamped edge under a uniformly distributed load are solved using the load superposition method and the orthotropic plate theory. The CSPRP is calculated as an equivalent isotropic cast-in-place twoway slab using the transformation of function, and the application of the equivalent span ratio. The simplified elastic design method is presented for a CSPRP with three supported edges and one clamped edge under a uniformly distributed load. The elasticity coefficients of the CSPRP with the equivalent span ratio, ranging from 0.5 to 1.0 and stiffness ratios of 0.5 and 2 are obtained using the programming calculation. The linear interpolation method is applied using the equivalent span ratio of an isotropic cast-in-place two-way slab, and one example of a CSPRP with three supported edges and one clamped edge is given to verify. The results show that the simplified elastic design method is accurate and feasible.concrete composite slab, elastic design method, orthotropic characteristic, three supported edges and one clamped edge, two-way slab | INTRODUCTIONA concrete composite slab is composed of precast ribbed panels and a cast-in-place concrete topping. It has been widely used in the construction of floors in building structures and decks in bridges because of its fast building assembly, significant time and labor savings, and good integrity and seismic performance. [1][2][3][4] Concrete composite slabs can be classified in a variety of ways. For example, composite slabs with precast concrete bottom panels, which are divided into solid plates, hollow plates, and T-shaped plates 5 ; composite slabs with a rough surface or with shear connectors. 6 Extensive efforts have been made on the composite slabs with precast concrete bottom panels, to investigate the interface shear performance between precast panels and cast-in-place concrete. The reported results include: (1) precast panels with naturally rough surfaces met the requirements of shear bearing capacity under the service load 7-9 ; (2) shear connectors took effect only when a bond slip occurred beyond the service load. 10,11 The horizontal shear strength at the interface between concrete surfaces has also been studied extensively. [12][13][14][15][16][17][18][19][20] These studies mainly focused on the effect of concrete strength and the type of surface treatment on the interface shear strength. As these studies were mostly conducted toward understanding of the shear friction theory, the specimens usually included a dowel reinforcement crossing the interface. The experimental findings obtained from these studies can be used to evaluate the accuracy of horizontal shear strength equations available in se...
Passive houses have strong thermal insulation and airtightness of doors and windows, and they are generally used in cold climates. This case study aims to evaluate the energy-saving potential of this technology in the hot-summer and cold-winter areas (Cf in Köppen climate classification) of China. The results show that after enhancing the thermal insulation and airtightness, the energy consumption in winter significantly decreased by 62% overall. However, the energy consumption of cooling in the transition season and summer increased, which is caused by overheating. Hybrid ventilative cooling and shading can solve this problem. In particular, when the indoor temperature range is set to the adaptive thermal comfort of natural ventilation, the energy consumption from air conditioner cooling can be greatly reduced by 81% overall. Passive houses combined with ventilative cooling has significant application value in this climate zone.
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