Longitudinal Shear Failure Research Articles

Hardwood and softwood timber - natural stone composite connections

This paper describes fabrication and testing to ultimate of timber-stone composite (TSC) connections using unreinforced limestone slabs fastened to hardwood or softwood stubs by screws at 45° or 90° to the interface, bonded-in meshes or interface bonding. The stone’s tensile strength prevented crack-formation during drilling or grooving of holes to accommodate the screws and meshes. Connections failed by splitting of the stone along the connectors (meshes, 90° screws in hardwood), pullout of 45° screws from softwood (S45), shear-flexure yield fracture of 90° screws in softwood (S90), longitudinal shear failure of softwood adjacent to interface adhesive, and tensile yield fracture of 45° screws in hardwood (H45). In descending order the glued, H45 and mesh connections were the strongest while the glued, meshed and 45° screw connections exhibited the highest slip stiffnesses, with the S90/S45 connections showing the most ductility. Likely influences of randomness in the stone’s tensile strength and in observed bond variabilities from fabrication of the mesh connections are discussed. The TSC connections performed well against timber-concrete composite connections. Stiffness predictions incorporating screw axial and lateral contributions are excellent for H45 and S90, but need improvement for S45 and H90. Strength predictions work well for all screw connections. These TSC connections can significantly reduce consumption of the natural materials stone and timber in low-carbon composite floor systems.

Experimental investigation on the structural behaviour of novel non-metallic pultruded circular tubular GFRP T-joints under axial compression

Different uniplanar T-joints made from pultruded glass-fibre reinforced polymer (GFRP) circular tubular sections (CHS) incorporating different innovative non-corrosive reinforcements with structural adhesives, carbon-fibre laminates (CFRP) and concrete-filled GFRP rods were developed, and their structural performance was tested under axial compression. The hollow T-joints without any connection reinforcements displayed brittle failure with out of plane longitudinal shear failure while the ones reinforced with CFRP and concrete-filled GFRP rods shows superior ultimate strength and ductility with diverse failure modes including interlaminar failure within the pultruded chord. With CFRP wrapping and concrete filling, increases in strength and ductility of up to eightfold and fortyfold were seen, respectively. Design oriented equations and analytical formulations were developed for the T-joints and their predictions were compared with experimental results. These novel connections presented in this study are recommended for future construction of offshore tubular structures.

Karakteristike posmične veze u spregnutoj ploči od čelika i betona

Steel-concrete composite slabs with cold-formed, profiled steel deck sheets are popularly used in steel-framed buildings. In these slabs, the deck platform acts as a working platform during construction and also as tensile reinforcement under in-service load conditions. The shear bond capacity of the composite slab is evaluated in this study for two different profile steel deck sheets. Specifically, their composite behaviour is investigated by casting and testing twelve full-scale composite deck slab specimens using the two-point loading system. In addition, based on the shear span length and profile height, the structural performance of the composite deck slab is analysed in terms of load-displacement response, shear bond capacity, ductility index, and load-slip behaviour. The results show that the most common failure of all tested specimens occurs due to the longitudinal shear failure between the concrete and profile deck sheets. As the longitudinal shear is a complex phenomenon, empirical approaches are used to evaluate the shear bond mechanism between the concrete and profile deck. The verification and comparison of experimental test results are performed with conventional and simplified m-k models based on the profile deck depth. The validated results reveal an acceptable level of reliability for prediction of each profile height based on the m and k interaction values.

Experimental study and prediction model for bond behaviour of steel-recycled aggregate concrete composite slabs

Using recycled aggregate concrete in a composite slab among the most promising solutions to effectively increase the utilisation of construction and demolition waste concrete. Longitudinal shear failure is a critical failure mode of composite slabs directly determined by the interfacial bond behaviour between concrete and profiled steel decks. However, the influence of recycled concrete aggregate (RCA) on interfacial bond behaviour remains unclear. Thus, this study conducted a pull-out test on the interfacial bond behaviour of composite slabs on 15 groups of specimens considering variables of replacement ratios of RCA (0, 50, and 100%), water-to-cement ratios (0.31, 0.45, and 0.60), steel deck thicknesses (0.8, 1.0, and 1.2 mm), and steel deck rib heights (48 and 65 mm). The bond-slip curves for all slabs were obtained, based on which the failure mechanism and influence of RCA under different parameters were discussed. Finally, an empirical prediction model for the bond-slip curve was established on the basis of the test data. The results showed that (1) the failure mode of composite slabs was independent of RCA, while the decrease in the steel deck rib heights induced more cracks in the failed slabs; (2) incorporating RCA decreased the ultimate bond stress by 4%–20% and the stiffness by 8%–14%; (3) the influence of RCA was coupled with other parameters; and (4) the proposed model exhibited a good prediction capability for the bond-slip behaviour of steel-RAC composite slabs.

Flexural behavior of assembled monolithic long-span composite beams with CIP reinforced concrete layer atop precast hollow core slabs

Steel-concrete composite beams (CB) with precast hollow-core slabs (HCSs) have been widely used in long-span structures for its high bending capacity, good ductility, lightweight, and fast construction. A novel assembled monolithic CB with a cast-in-place (CIP) reinforced concrete layer poured on the precast HCSs (CBCH) was proposed in this study. Eight full-scale flexural tests were conducted majoring in the parameters of span (L = 6.0 m and 8.4 m), degree of shear connection (λDS = 100%, 70%, and 30%), width of CBCH (B = 2100 mm and 1800 mm), and thickness of CIP concrete layer (hCIP = 60 mm and 20 mm). Three typical failure modes were observed: i.e. flexural failure, longitudinal shear failure in the shear span, and peeling failure occurring between the precast HCS and CIP concrete layer. The results indicate that the λDS and hCIP can significantly affect the failure modes, flexural capacity, and ductility; the B has a slight influence on the bending behavior of CBCH. In addition, an extensive parametric study was conducted according to the test results. To elevate the bending capacity of CBCH, relative formulas are proposed, and agree well with the results of test and parametric study. Based on the theoretical and FE analysis, the partial shear specimens with λDS ≥ 85% can achieve almost the same performances as the full shear specimens (λDS = 100%). However, a λDS = 100% and the minimum hCIP = 60 mm are recommended to ensure the integrity of the CBCH in engineering practice.

Behavior of sinusoidal-corrugated-steel-plate–concrete composite slabs: Experimental investigation and theoretical model development

Composite slabs with trapezoidal steel sheets have been extensively used in composite flooring systems. Sinusoidal steel sheets can be fabricated with relatively thicker steel plates and employed in smooth-curved structures such as buried culverts, thus exhibiting a relatively wider application range than trapezoidal steel sheets. Study has rarely been conducted on composite slabs composed of concrete cover and relatively thick sinusoidal corrugated steel plates. This study focus on the bending behavior and longitudinal shear mechanism of composite slabs with sinusoidal corrugated steel plates. Four-point bending tests were conducted considering different slab thicknesses, shear connector types, and numbers. Partial interaction theory was adopted as the basis for the development of the corrugated-steel-plate–concrete composite slab theoretical model. A computer program named CSPC-SSA (Corrugated-Steel-Plate–Concrete Simply-supported Slab Analysis) was written based on partial interaction theory and finite difference method. The Modified Newton-Bisection algorithm was developed to balance the calculation time and accuracy. It can be concluded that the newly proposed shear connector exhibits similar strength and deformation behavior compared to the conventional shear connector, and that the flexural strength of the corrugated-steel-plate–concrete composite slab was positively correlated with the shear connector number and concrete cover thickness. Improperly increasing the concrete cover thickness may cause longitudinal shear failure.

Experimental study of flexural behaviour of high strength steel (HSS) ‐ Engineered Cementitious Composites (ECC) composite beam with profiled steel sheeting

AbstractDue to its high compressive strain of at least 0.5%, which is higher than both the yield strain (0.35%) of high strength steel (HSS) and the compressive strain (0.23%) of normal strength concrete (NSC), Engineered Cementitious Composites (ECC) is a material with high potential to replace NSC in HSS composite beam construction. This study reports an experimental investigation on the flexural behaviour of HSS‐ECC composite beam fabricated by using HSS I‐section in conjunction with hybrid polyethylene‐steel fibers (PE‐ST) ECC slab. Shear connection between the HSS I‐section and the top PE‐ST ECC slab was constructed by using normal profiled steel sheeting and headed shear studs. A HSS‐ECC composite beam and a HSS‐NSC composite beam were cast and tested under four‐point bending. The test results revealed that a large area of HSS I‐section in HSS‐ECC composite beam yielded compared to only a small yielded area of which in the HSS‐NSC counterpart despite the fact that both composite beams have identical configuration and silimar mechanical properties. The HSS‐NSC beam underwent longitudinal shear failure while in contrast, the HSS‐ECC beam failed by flexure and exhibited great ductility.

Study on the ductility of open‐rib and re‐entrant composite slabs

AbstractComposite slabs with profiled steel sheeting and cast‐in‐place concrete are a conventional structural flooring system worldwide. The partial connection method (PCM) is a design method limited to slabs showing a ductile longitudinal shear failure. The ductility is defined in Eurocode‐4 in terms of additional strength after certain initial slip is produced, regardless of the steel sheet profiling shape. This article shows that the slip behavior is significantly different depending on the shape of the sheeting profile. On the one hand, the slip magnitude in reentrant slabs can be large enough to drive the two materials to their yielding stresses; on the other hand, in open‐rib profiles, the slab failure is due to the vertical release of the concrete, when the slip overpasses certain geometric limit. This failure mode is generally produced much before the materials reaches their yielding stresses. This finding is consistent with both the experimental and FEM results carried out in this study.

Contribution of steel sheeting to the vertical shear capacity of composite slabs

The real capacity of steel-concrete composite slabs currently used in buildings tends to be governed by the longitudinal shear failure mode. However, in many cases, the design of these structural members according to Eurocode 4, Part 1.1 (EN 1994-1-1) is governed by the vertical shear capacity. The design methodology for the determination of the vertical shear resistance predicted in the referred standard underestimates the shear resistance of steel-concrete composite slabs because it is based on the design model for reinforced concrete slabs stated in Eurocode 2, Part 1.1 (EN 1992-1-1), does not take the contribution of the profiled steel sheeting into account adequately. The results of an experimental programme, comprising 4 experimental tests on short-span steel-concrete composite slabs and carried out at the Department of Civil Engineering of the University of Coimbra, Portugal, are then shown and discussed. In order to induce a failure by vertical shear, the composite slabs tested were provided with a longitudinal shear reinforcement system composed by transversal bars crossing longitudinal stiffeners placed along the upper flange of the steel sheets. The results of the experimental tests were also used to calibrate numerical models, which made it possible to carry out a parametric analysis. The experimental and numerical results showed that the design methodology prescribed by Eurocode 4, Part 1.1 is quite conservative as it underestimates the relevant contribution of the resistance of the profiled steel sheeting to the slab's vertical shear capacity.

Flexural behavior of high-strength steel hybrid composite beams

In this study, hybrid utilization of high-strength steel in composite beams was proposed in order to maximize their flexural capacity and full-scale testing was conducted in two phases to investigate their flexural behavior. In fabricating specimens, high-strength steels were utilized for the bottom flange while normal-strength steels were used for the top flange and the web. In Phase I testing, however, all the high-strength steel bottom flange specimens were not able to reach their plastic moment by about 10–15% due to unexpected longitudinal shear failure along the beam axis, although sufficient shear studs were provided for full composite behavior and the plastic neutral axis location was limited within 15% of the total depth of the composite beam section. The specimens in Phase II testing designed with additional shear reinforcements showed no longitudinal shear cracking and developed their plastic capacity with reasonable deformability as intended in design. This implies that, different from the design of conventional composite beams, checking the longitudinal shear strength of composite concrete slab is crucial when designing hybrid composite beams utilizing high-strength steels. The nominal longitudinal shear strength was well predicted by the shear-friction based models in ACI 318-14 and AASHTO LRFD. The test results of this study show that when the limitation on the depth of the plastic neutral axis set forth by Eurocode 4 is satisfied along with sufficient longitudinal shear strength, the plastic stress design method can still be applied to the design of hybrid composite beams utilizing high-strength steels whose nominal yield strength is as high as 650 MPa.

Experimental and finite element study of ultimate strength of continuous composite concrete slabs with steel decking

Composite one-way concrete slabs with profiled steel decking as permanent formwork are commonly used in the construction industry. The steel decking supports the wet concrete of a cast in situ reinforced or post-tensioned concrete slab and, after the concrete sets, acts as external reinforcement. In this type of slab, longitudinal shear failure between the concrete and the steel decking is the most common type of failure at the ultimate load stage. Design codes require the experimental evaluation of the ultimate load capacity and longitudinal shear strength of each type of steel decking using full-scale tests on simple-span slabs. There is also no procedure in current design codes to evaluate the ultimate load capacity and longitudinal shear strength of continuous composite slabs and this is often assessed experimentally by full-scale tests. This paper presents the results of three full-scale tests up to failure on continuous composite concrete slabs cast with trapezoidal steel decking profile (KF70) that is widely used in Australia. Slab specimens were tested in four-point bending at each span with shear spans of span/4. The longitudinal shear failure of each slab is evaluated and the measured mid-span deflection, the end slip and the mid-span steel and concrete strains are also presented and discussed. Redistribution of bending moment in each slab is presented and discussed. A finite element model is proposed and verified by experimental data using interface element to model the bond properties between steel decking and concrete slab and investigate the ultimate strength of continuous composite concrete slabs.

Experimental evaluation of longitudinal splitting of bamboo flexural components

Splitting or longitudinal shear failures in full-culm bamboo are a critical limit state when using the material for construction applications. Understanding and quantifying the behaviour must be through standardised test methods for international adoption into building practices to be successful. Current testing procedures only determine an effective flexural strength due to splitting failures. The present study investigates longitudinal shear failure in full-culm Phyllostachys pubescens (Moso) and Bambusa stenostachya (Tre Gai) bamboo flexural specimens through a number of standard and modified test methods. In particular, the paper proposes modifications to ‘standard’ culm flexural tests intended to better capture actual shear-dominated behaviour. Notched specimens were used to better establish relationships between mode I and mode II behaviours. The test results illustrate the significant degree of interaction between mode I and mode II stresses resulting from flexural tests and their associated failures, specifically the significant deterioration of mode II capacity in the presence of even a small amount of mode I stress. It is proposed that a uniform experimental approach using horizontally notched flexural specimens having different shear spans and notch locations would be appropriate to establish a relationship between mode I and II behaviour.

Experimental investigation of longitudinal shear behavior for composite floor slab

This paper presents an experimental study on the behavior of composite floor slab comprised by a new steel sheet and concrete slab. The strength of composite slabs depends mainly on the strength of the connection between the steel sheet and concrete, which is denoted by longitudinal shear strength. The composite slabs have three main failures modes, failure by bending, vertical shear failure and longitudinal shear failure. These modes are based on the load versus deflection curves that are obtained in bending tests. The longitudinal shear failure is brittle due to the mechanical connection was not capable of transferring the shear force until the failure by bending occurs. The vertical shear failure is observed in slabs with short span, large heights and high concentrated loads subjected near the supports. In order to analyze the behavior of the composite slab with a new steel sheet, six bending tests were undertaken aiming to provide information on their longitudinal shear strength, and to assess the failure mechanisms of the proposed connections. Two groups of slabs were tested, one with 3000 mm in length and other with 1500 mm in length. The tested composite slabs showed satisfactory composite behavior and longitudinal shear resistance, as good as well, the analysis confirmed that the developed sheet is suitable for use in composite structures without damage to the global behavior.

Novel cellular perlite–epoxy foams: Effect of density on mechanical properties

A novel type of economical lightweight foam with density from 0.15 to 0.45 g/cm3 was made from a high volume fraction of expanded volcanic glass (perlite) in an epoxy matrix. The compressive strength, effective elastic modulus, and modulus of toughness of the foams all increased with the foam density. The strength increased linearly, peaking at 1.7 MPa whereas the effective elastic modulus and modulus of toughness increased at parabolically increasing and decreasing rates, respectively. The specific compressive stress of the newly developed foam in the density range of 0.3–0.44 g/cm3 is comparable with foams made from alumina, aluminium–silicon carbide, closed cell phenolic resin, and closed cell polypropylene. Post-test SEM observations coupled with photogrammetry during the tests revealed three different failure modes: longitudinal splitting, shear failure, and compression failure were present over the whole density range. The material was found to be a good candidate for the stiffening cores within sandwich panels.

Composite Slabs with Prepressed Embossments – Longitudinal Shear Resistance

Composite slabs with prepressed embossments present an effective solution for horizontal structures. Prepressed embossments ensure composite action after hardening of concrete. Longitudinal shear failure mode typically governs if the shear resistance of embossments is not sufficient for full composite action. Mutual separation of thin-walled sheeting from concrete and its deformation inside the rib is characteristic for this failure mode. Design methods for composite slabs use full scale bending tests in several series to determine their bearing capacity. A less expensive alternative is to use small-scale shear tests to determine shear characteristics of the sheeting. This paper presents detailed numerical models of slab in shear and models of slab in bending with and without embossments. These models are compared with previously performed experiments. Key WordsComposite slab; steel sheeting; concrete; prepressed embossment; longitudinal shear; experiment; numerical model

Longitudinal shear stress and bond–slip relationships in composite concrete slabs

Composite one-way concrete slabs with profiled steel decking as permanent formwork are commonly used in the construction industry. The steel decking supports the wet concrete of a cast-in-situ reinforced or post-tensioned concrete slab and, after the concrete sets, acts as external reinforcement. In this type of slab, longitudinal shear failure between the concrete and the steel decking is the most common type of failure at the ultimate load stage. Design codes require the experimental evaluation of the longitudinal shear capacity of each type of steel decking using full scale tests.This paper presents the results of the short term testing up to failure of four types of profiled decking that are widely used in Australia. Full-scale, simply-supported slab specimens were tested in four-point bending with shear spans of either span/4 or span/6. The bond–slip relationship of each slab was determined during the testing and the values of maximum longitudinal shear stress calculated using different methods are described and compared. A finite element model is proposed and verified by experimental data using interface element to model the bond properties between steel decking and concrete slab and investigate the ultimate strength of composite slabs.

Iterative determination of threshold FRP area needed to avoid non-ductile longitudinal shear failures in yield-zones of FRPRC members

This paper presents a novel nonlinear iterative scheme to determine threshold areas of FRP plating which avoid longitudinal shear failure of the FRP-to-concrete connection in yield zones of FRPRC beams. Implicit differentiation of an experimentally-verified predictive model for longitudinal shear failure and of associated FRPRC section equations is used to generate incremental expressions which underpin the iterative scheme. Iterations are driven by the disparity between the longitudinal shear stress for the updated area of plate and the connection’s longitudinal shear strength. For different load types on a FRPRC beam, the scheme is shown to exhibit robust convergence characteristics in regimes of pronounced nonlinearity, with reliable gravitation toward the correct plate area from a wide range of starting values of this plate area. The study produces the counter-intuitive result that stiffer plates reduce longitudinal shear requirements, probably owing to the associated shorter yield zones of reduced yield activity at the specified peak load of the FRPRC member.

Experimental investigations on composite slabs to evaluate longitudinal shear strength

Cold-formed steel profile sheets acting as decks have been popularly used in composite slab systems in steel structural works, since it acts as a working platform as well as formwork for concreting during construction stage and also as tension reinforcement for the concrete slab during service. In developing countries like India, this system of flooring is being increasingly used due to the innate advantage of these systems. Three modes of failure have been identified in composite slab such as flexural, vertical shear and longitudinal shear failure. Longitudinal shear failure is the one which is difficult to predict theoretically and therefore experimental methods suggested by Eurocode 4 (EC 4) of four point bending test is in practice throughout world. This paper presents such an experimental investigation on embossed profile sheet acting as a composite deck where in the longitudinal shear bond characteristics values are evaluated. Two stages, brittle and ductile phases were observed during the tests. The cyclic load appears to less effect on the ultimate shear strength of the composite slab.

Development of interlocking mechanism for shear transfer in composite floor

Semi-pre-cast floor slab (called half slab in Malaysia) has been used widely in different parts of the world. It consists of a reinforced concrete pre-cast layer that acts initially as a formwork connected in situ with another concrete layer using shear connectors. Steel reinforcement (shear link, studs and/or steel truss) is commonly used to transfer the horizontal shear between the two composite layers. Longitudinal shear failure is the most common type of failure in the composite floor slab. This paper proposes a new system to transfer the horizontal shear between the interfaces of the pre-cast and cast in situ layers of concrete slab. The proposed system implements an interlocking concept and does not require any shear reinforcement. The composite floor slab used to illustrate the interlocking concept consists of a pre-cast inverted ferrocement layer interconnected with the cast in situ brick–mortar layer. The effectiveness of the interlocking mechanism in transferring the stresses developed due to the applied load is investigated. Eleven composite slab specimens having different shear connectors between the two layers were cast and tested under pure shear loading (push-off test). In the tested specimens, different interlocking mechanisms, continuous truss shear connectors and no connectivity between the two layers were used to connect the layers of slabs. The results indicate that the interlocking mechanism proposed is, as effective as, the steel trusses in resisting shear stresses and can be used to replace the steel trusses, which in turn will reduce the cost of the composite slab.

Micro-Mechanics of Failure (MMF) for Continuous Fiber Reinforced Composites

The micromechanics of failure was developed to predict the failure of continuous fiber reinforced composites. A micromechanical approach using unit cells of square and hexagonal arrays was employed to compute the micro stresses of constituents and at the fiber—matrix interface, which were used to determine the failure initiation of a unidirectional ply. The constituent properties include two tensile and compressive strengths of fiber and matrix, plus normal and shear strengths at the interface. The matrix and interfacial dominated strength properties are determined by matching the micro stresses at the constituent levels with the observed transverse tensile and compressive strengths on the macro ply level. The longitudinal shear failure is then expected to be a result of damage progression after initial failure. Based on the current MMF, in the graphite/epoxy considered in this study both transverse tensile and compressive failure are expected to occur via matrix failure. However, in the glass/epoxy the transverse tensile and compressive failures are respectively caused by matrix failure and interfacial tensile failure. These predictions are compared with predictions from other widely used failure criteria as well as experimental data. Lastly, we predicted the failure of laminates. Instead of using a unidirectional ply-based failure theory, starting with the fiber, matrix, and their interface will lead to a much simpler, more generic theory.