Composite members have been widely used in the construction of medium- and high-rise buildings. The results of the development of a new structural member by experimental investigation of the flexural behavior of hollow composite beams are presented in this paper. This research aims to exploit the properties of composite sections and their strength in developing a new approach for overcoming the problems of service pipes in buildings. A hollow steel section encased fully in concrete is used to form a composite hollow beam. The structural benefit provided by the steel section (composite part) is adopted to increase the stiffness of the member. The hollow part is employed to provide services and economic benefits by reducing the amount of expensive ultra-high-performance concrete (UHPC) used and decreasing the self-weight of the member. The flexural strength of 11 UHPC beams is tested under two-point loads. The variables in this investigation include the type of hollow core mold material and the size, location, and shape of steel hollow sections in the middle and tension zones of the cross-section. Experimental results are compared and discussed. The tested results show that the flexural capacity and stiffness of the UHPC-encased steel hollow beams are 109% and 23.5% higher than those solid beams, respectively.
Estimating the shear strength of Ultra-High-Performance Concrete (UHPC), with high compressive and tensile strengths, is complicated by many variables that affecting its behavior. Residual tensile stress (RTS) plays an important role in raising the efficiency of both types of resistance, especially shear strength due to the presence of steel fibers, which makes it difficult to quantify the residual tensile stress due to the different failure patterns of these fibers and the distribution mechanism within the concrete matrix. There is no study to date in assessing residual tensile stress of UHPC structural members of the variable section. Thirteen beams were selected as an experimental program to study six main variables in determining shear strength. Stirrups ratio, flexural reinforcement ratio, the volumetric fraction of steel fibers, geometry changing, existing openings along the longitudinal axis, and shear span to depth ratio. According to on Tests results, RTS is compatible with most of the global specifications.
In this paper, a new masonry construction is proposed based on honey beehive cell internal geometry as a unique structure and hydrostatic pressure principle. The considered experimental program involved suggestion, manufacturing, testing and analysis of masonry specimens of honey beehive units’ arrangement as well as corresponding specimens of custom arrangement, two classes of cementations bonding mortars are used. Plan strain concept and Saint Venant’s principle are adopted to model and assign proper boundary conditions of testing specimens. The significant improvement of masonry construction bearing capacity is confirmed by the obtained results and could be related to the presence of internal or self-confining pressure, which is produced due to the specific internal geometry of proposed honey beehive units’ arrangement of hexagonal construction units. The obtained results show that, the masonry specimens of proposed honey beehive arrangement Mode II exhibited higher bearing capacity in term of ultimate and service loads besides stiffness improvement in comparison with the customary arrangement Mode I.
The hollow structural elements occupy a great deal of researchers’ interest due to the possibility of losing their weights and maintaining or developing their resistances especially when increasing both compressive and tensile strength of modern materials. The flexural strength based on the forces balance and stain compatibility was derived. Nine beams of Ultra High Performance concrete (UHPC) and conventional reinforced steel bars were casted. Several parameters were taken which are the thickness of the concrete top flange, thickness of the concrete bottom flange, depth of the longitudinal hollow and the ratio of the longitudinal reinforcing steel. By comp aring the practical and theoretical results, the proposed flexural strength provided a safety factor of one-fifth against the experimental collected data. The ultimate flexural force developed up 260 % when increasing the reinforced steel area 4.6 times and 230 % comparing with the solid beam. Many aspect ratios were also mentioned that keep the strength in developing.
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