A semi-analytical procedure is presented for predicting the complete flexural response of partially interacting steel-concrete composite beams up to failure. The governing equation of the Euler-Bernoulli beam theory is solved wherein concrete, steel and the shear connectors joining the concrete slab to the steel beam are assumed to have nonlinear stress-deformation relationships. The adopted constitutive relationship for the connectors allows for partial or full composite action. The solution is applicable to beams and one-way slabs subjected to concentrated or uniform load and/or their combination. The governing equation is numerically solved by satisfying the equilibrium and compatibility requirements along the member. For the reinforced concrete slab part of the composite beam, nonlinear moment-curvature and axial force-extreme concrete fiber strain relationships are developed that account for concrete nonlinearity in compression and for cracking and tension-stiffening in tension as well as for steel reinforcement nonlinearity. Comparison of the proposed model results with the corresponding experimental load-deflection curves and interfacial shear-slip curves of several beams tested by others show good agreement between them. The relative simplicity, efficiency and easy application of the present solution make it possible to accurately predict the failure load, interfacial slip and full nonlinear response of partially interacting composite beams.
Four large scale concrete beams of 4.2 m length and 200 x 500 mm cross-section were built and tested under four-point bending. Two beams were used as control beams and were reinforced with mild steel for both shear and flexure. The flexural and shear reinforcement for the remaining two beams were provided by externally bonded carbon fibre (CFRP) sheet. In addition, to achieve ductility in the CFRP reinforced beams, a low modulus high strain high density polypropylene grid (HDPP) was placed within them. The primary focus of this study was to achieve ductility via the provision of HDPP but it was also intended to prevent delamination of bonded CFRP sheets by attaching some of the laminae to the sides of the beam rather than attaching them all to the beam soffit. Finally, the magnitude of shear that could be resisted by externally bonded CFRP U stirrups was investigated. The hybrid reinforced beams achieved their design capacity and initial failure occurred due to rupture of CFRP sheet in the maximum moment region, followed by some delamination. The CFRP stirrups reached 70% of their ultimate strain capacity. After the rupture of CFRP, the HDPP provided the beams with residual strength, but due to the low modulus of HDPP, the deformations of the beams increased substantially. (A) For the covering abstract see ITRD E104933.
This paper presents the results of an analytical investigation of one-way unreinforced masonry (URM) walls retrofitted with externally anchored steel studs and subjected to blast loads. Using the wall geometrical and material properties, deflected shape, and crack pattern as input, a nonlinear model is developed to predict the inward force-displacement relationship of the retrofitted walls. In addition, using a rigid body analysis, a simple bilinear force-displacement relationship is developed to model the outward force-displacement relationship of the walls. Utilizing these two force-displacement relationships (resistance functions), a generalized single-degree-of-freedom (SDOF) model is developed to capture the nonlinear out-of-plane dynamic response of the retrofitted walls under blast loads. The SDOF model captured the experimentally observed displacement responses of the tested walls with reasonable accuracy. The model was also used to investigate the influence of block thickness, wall slenderness ratio, blast load intensity, and blast pulse shape on the out-of-plane dynamic response of retrofitted walls. The results demonstrated that anchored steel-stud systems could significantly enhance the out-of-plane capacity of the retrofitted walls by increasing their out-of-plane capacity and reducing their displacement.
New method of mixture proportioning is proposed for concrete made with coarse recycled concrete aggregates (RCA). The proposed method, dubbed the "equivalent mortar volume" method, is predicated on the fact that RCA is a two-phase material comprising mortar and natural aggregate; therefore, when proportioning a concrete mixture involving RCA, one must account for the quantity and quality of each phase and adjust both the coarse aggregate and fresh paste content of the mix accordingly to achieve the same total mortar volume as a companion mix with the same specified properties but made entirely with coarse natural aggregates of similar properties to the coarse natural aggregate contained in RCA. Using the proposed method and the conventional aggregate replacement method, a large number of mixes was made with RCA obtained from two demolition waste recycling plants. For each mix, its slump, fresh and hardened densities, compressive strength, and elastic moduli were measured. The results showed that using the proposed method, unlike the conventional method, yields concrete mixes with consistent, predictable, and comparable properties to those of similar mixes made with natural aggregates.
Premature deterioration of concrete structures has created awareness and concern about the durability of concrete. Concrete mixtures used in the construction of residential basement walls and foundations have a high water to cement (w/c) ratio (w/c>0.6) and low cement content (<280kg/m3). The result is friable concrete with a highly porous surface layer and high potential for cracking. The defects have a direct impact on the durability of concrete. This experimental study examines the effects of three parameters—mix design, formwork, and consolidation—on the quality of the surface of high w/c concrete. The fresh concrete is characterized using its rheological properties—in particular, its yield stress and plastic viscosity. Pulse velocity, pull-off strength, and compressive strength were measured to evaluate the quality and the mechanical properties of the hardened concrete. The durability of the hardened concrete was evaluated by measuring its surface transport properties—namely, its air permeability and sorptivity. The results show that it is possible to correlate the rheological properties of fresh concrete to the mechanical and permeation properties of the hardened concrete.
