Design Shear Resistance Research Articles

Reliability-based design shear resistance of headed studs in solid slabs predicted by machine learning models

The economical and reliable design of steel-concrete composite structures relies on accurate predictions of the resistance of headed studs transferring the longitudinal shear forces between the two materials. The existing mechanics-based or empirical design equations do not always produce accurate and safe predictions of the stud shear resistance. This study presents the evaluation of nine machine learning (ML) algorithms and the development of optimized ML models for predicting the stud resistance. The ML models were trained and tested using databases of push-out test results for studs in both normal weight and lightweight concrete. The reliability of ML model predictions was evaluated in accordance with European and US design practices. Reduction coefficients required for the ML models to satisfy the Eurocode reliability requirements for the design shear resistance were determined. Resistance factors used in US design practice were also obtained. The developed ML models were interpreted using the SHapley Additive exPlanations (SHAP) method. Predictions by the ML models were compared with those by the existing descriptive equations, which demonstrated a higher accuracy for the ML models. A web application that conveniently provides predictions of the nominal and design stud shear resistances by the developed ML models in accordance with both European and US design practices was created and deployed to the cloud.

Shear enhancement in RC beams without shear reinforcement simultaneously loaded within 2d and at 3d from supports

Shear resistance is increased by arching action when reinforced concrete (RC) beams are loaded within around twice the beam effective depth (d) of supports. The vast majority of laboratory tests have investigated shear enhancement in beams under three- or four-point loading with all loads applied within 2d of supports. This type of loading is representative of deep beams but not slender beams and slabs which are invariably loaded within the span when subject to point loads near supports. The latter problem arises in many guises in practice but is scarcely researched. The motivation for looking into the problem was the difference in design approaches adopted in EC2 and the superseded UK code BS8110. The former accounts for shear enhancement by reducing the design shear force while the latter increases the design shear resistance within 2d of supports. The UK National Annex to Eurocode 2 Part 2 Concrete Bridges adopts the approach of BS8110 for members without shear reinforcement. The paper presents the results of tests on four simply supported RC beams without shear reinforcement in which the loading arrangements were chosen to investigate the influence on shear enhancement of applying loads both within and outside 2d of supports. Digital image correlation (DIC) system was used to investigate the crack kinematics and shear resisting mechanisms of each beam. The BS8110 approach to shear enhancement is shown to be potentially unsafe for beams without shear reinforcement. Good predictions of strength were obtained with EC2 as well as strut and tie modelling in which the concrete strength was determined using the Modified Compression Field Theory.

Development of Shear Resistance Formula for the Y-Type Perfobond Rib Shear Connector Considering Probabilistic Characteristics

A design shear resistance formula for Y-type perfobond rib shear connectors is proposed with the various reduction factors, which can be selected depending on the target safety level. The nominal shear resistance formula is improved based on the systematic sensitivity analysis as well as the regression fit test based on 84 push-out test results, including 15 additional push-out tests to extend the application ranges and reduce the estimation errors, compared to the formula proposed in previous studies. Some design variables are additionally included in the proposed design formula: the yield strengths of rebar and rib plate. The basic design variables in the proposed design formula are (1) number of ribs and transverse rebars, (2) concrete compressive strength, (3) rebar diameter and yield strength, and (4) rib thickness, width, height, and yield strength. The application ranges of the basic design variables are recommended for the proposed design formula. The various shear resistance reduction factors are proposed based on the probabilistic ultimate shear resistance model of Y-type perfobond rib shear connectors. The proposed procedure may be recommended to develop the design formula for shear connectors with various shapes.

Comparison between Theoretical and Experimental Investigation of Composite Beams with Spiral Shear Connectors.(Dept.C)

Investigation of the behavior of composite beams with different types of shear connectors (spirals and bent bars) extends to include the comparison between the theoretical study and the experimental results of such types of beams. In this paper, a proposed technique for predicting the shear resistance of the spirals as shear connectors in the composite beams is presented. In this- technique, the behavior of the connectors in the elastic and the plastic ranges is analyzed. Hence, a proposed formula to predict the design shear resistance of the spirals is suggested. The comparison between the suggested formula and the experimental results showed a good agreement between them. Moreover, a comparison between the theoretical and the experimental results for the tested composite beams with spirals and bent bars as shear connectors is carried out with respect to ultimate loads. ultimate moment and deflections. The common type of shear connectors as bent bars is compared with spiral connectors as well. A discussion for the given formulae of die beat bar shear resistance in both Egyptian and European (EC4) codes together with the experimental results is conducted which may lead to the modification of the Egyptian formula. The comparison between the present theoretical work and the experimental results has shown good agreement.

New approach for the design shear resistance of headed studs in profiled steel sheeting with ribs transverse to supporting beam

New approach for the design shear resistance of headed studs in profiled steel sheeting with ribs transverse to supporting beam

Vertical and horizontal push tests on specimens with a Trefoil decking profile

The vertical push test has historically been the primary means used to evaluate the strength of shear connectors used in steel-concrete composite floors; however, these tests can be difficult to conduct and generally their results have been shown to not well represent the behaviour of shear connectors in a full sized composite beam. This paper describes a series of twenty-four push tests on composite beam specimens with Trefoil profile steel decking and headed, through-deck welded shear connectors (shear studs) using two different test set-ups. Twelve push tests on specimens with 19 mm and 22 mm shear studs were conducted using the double sided vertically oriented setup from AS/NZS 2327 and Eurocode 4, with transverse load applied across the slab faces. Twelve further push tests were conducted on specimens with 19 mm diameter studs using a new horizontal set-up. The results of the vertical tests suggest that the equations in Eurocode 4 for the determination of design shear resistance may be unconservative for 19 mm and 22 mm shear studs in 80 mm deep Trefoil decking ribs. The horizontal test specimens showed the same poor post-peak load retention that is characteristic of push tests conducted using the vertical test set-up without the application of transverse load. These parallel test programs are an exploratory step towards understanding the differences in behaviour observed in vertical and horizontal push tests and are the initial efforts in a continuing research program to develop a horizontal push test that provides a close approximation of the behaviour observed in full-beam tests.

New approach for the design shear resistance of headed studs in profiled steel sheeting with ribs transverse to supporting beam

AbstractThis article presents new equations for the design shear resistance of headed studs in solid concrete slabs and new reduction factors that consider the influence of profiled steel sheeting with ribs transverse to the supporting beam. Comparisons with push‐out test results show that the current reduction factor kt in Eurocode 4 does not take sufficiently into account parameters such as geometry or position of the headed stud in the rib. Therefore, the mean shear test results are overestimated by the current equations. When introducing the new approach for the design resistance of headed studs, the main focus is on the description of the basic procedure for the development of the new approach and on the comparison with values in the existing code. Comparisons with push‐out test results from a recent European project have shown the good quality of the new approach.

Diaphragm action in light steel framing by sheathing boards

This paper presents the results of shear tests on light steel walls with two types of higher specification OSB/3 board and comparison with elastic theory based on the fixing shear stiffness. The tests were performed to BS EN 594 and showed that the design shear resistance was determined as 5.1 kN/m wall length for a limiting deflection of 0.003H or 4.3 kN/m for a limiting deflection of H/500, where H is the wall height. With plasterboard on the opposite face, the shear stiffness increased by 29%, but these results were more variable. For a single test on a wall with the OSB/3 board on one side and X bracing on the opposite face, the design shear resistance is 5.6 kN/m for a limiting deflection of H/500. For a flame retardant form of OSB/3 board, the stiffness was 21% higher than for the first series of OSB/3 tests. An elastic theory is presented to determine the limiting shear force as a function of the shear stiffness of the fixings between the boards and the C sections, which was provided from small-scale push tests. The results are compared with finite element models and a comparison with the test configurations is presented.

Shear strength of prestressed FRP reinforced concrete beams with shear reinforcement

To avoid brittle shear failures, the shear strength of reinforced concrete beams has to be verified at ultimate limit state. For this purpose, simple but accurate shear design provisions or shear resistance models are required. In current design provisions the influence of prestressing is either neglected or insufficiently considered in the design equations leading to rather conservative results due to the lack of investigations concerning the shear strength of FRP prestressed beams. To overcome this drawback, shear tests on concrete beams with textile shear reinforcement and pre-tensioned CFRP tendons were conducted and the results are presented in this paper. Besides the investigation of the influence of the level of prestressing and of the shear span-depth ratio on the shear strength, special attention was paid to the formation and the inclination of the shear cracks as well as the crack pattern to investigate the failure mechanism more in detail. Furthermore, theoretical investigations were conducted in order to derive a simple shear design model for prestressed concrete beams with FRP shear reinforcement. For this purpose, an existing shear resistance model based on a truss model with variable strut inclination is extended considering the beneficial effects of prestressing on shear strength.

Variable strut inclination model for shear design of FRP reinforced concrete members with shear reinforcement

To avoid brittle shear failures, the shear strength of reinforced concrete beams has to be verified at ultimate limit state. For this purpose, simple but accurate shear design provisions or shear resistance models are required. In this paper, the derivation of a simple shear design model for beams with FRP shear reinforcement is presented. At first, the suitability of existing code provisions and shear resistance models is evaluated using a large databank on shear tests on members with FRP shear reinforcement. Based on the results, a shear resistance model is developed based on a truss model with variable strut inclination, which is also the basis of the shear design of members with steel shear reinforcement according to current Eurocode 2. An important aspect regarding the derivation of the model is the definition of an appropriate method to determine the angle of the compression strut. For this purpose, a compression field model originally developed for steel reinforced concrete beams is adopted. The proposed resistance model is validated by means of a databank evaluation. Moreover, an equation to determine the minimum shear reinforcement ratio of FRP reinforced concrete members is derived based on the shear design provisions according to Eurocode 2.

Resistance of stud shear connectors in composite beams using profiled steel sheeting

In composite beam design, headed stud shear connectors are commonly used to transfer longitudinal shear forces across the steel-concrete interface. This paper describes the structural performance of shear connection in composite beams with profiled steel sheeting. An accurate and efficient nonlinear Finite Element (FE) model was developed to study the behavior of headed stud shear connectors welded through the deck. The concrete slab considered in this article uses profiled steel sheeting with ribs perpendicular to the longitudinal axis of the steel beam. The material nonlinearities were included in the FE model. The concrete was modeled considering a damaged plasticity model available in ABAQUS software. The results obtained from FE analysis were verified against experimental results. A parametric study was conducted to observe the effects of changing of both the stud position inside the rib of profiled steel sheeting and the concrete strength on the resistance of the stud shear connector. The shear resistance of stud connectors obtained from the FE analysis and many experimental push-out tests whose results are available in the literature were used as a database to compare with design shear resistance calculated using AISC-LRFD and Eurocode 4. It is found that the shear resistance of stud connectors, obtained from the design rules specified in these codes, in some cases is greatly underestimated, and in other cases significantly overestimated.

Design of 38m Span Post-tensioned Ultra High Performance Fiber-Reinforced Concrete (UHPFRC) Composite Bridge

Although ultra-high-performance fibre reinforced concrete (UHPFRC) has become commercially available in many countries, there are still limited design standards for UHPFRC structures. In 2016, the French Standard Institute has published the world first design standard for UHPFRC structures (NF P18-710) which is read conjunction with the UHPFRC material specification code (NF P18-470). This standard is the national complement to Eurocode 2 for the design of UHPFRC structures. To date, there have several UHPFRC bridges been designed by using this French Standard. The aim of this paper is to demonstrate working example on the design calculation of 38m span post-tensioned UHPFRC composite bridge using DURA® Grade140 which was recently constructed in Kuala Terengganu. The working example mainly focus on (i) the material properties input in the structural analysis software – Midas Civil; (ii) the output results on the design forces at the critical sections (mainly the design moment effect, MEd, and design shear force effect, VEd); (iii) the stresses of the post-tensioned UHPFRC U-girder at transfer, at different construction load history and at service stage (iv) the design moment resistance (MRd) and design shear resistance (VRd) of the composite section.

Working Example on 70m Long Ultra High Performance Fiber-Reinforced Concrete (UHPFRC) Composite Bridge

In 2016 the Association Française de Normalisation (AFNOR — French Standard Institute) has published the world first design standards for ultra-high-performance fibre reinforced concrete (UHPFRC) structures (i.e. NF P18-710:2016). This document is the national additional to Eurocode 2 for concrete structure design. To-date, there are several UHPFRC bridges have been designed using this standard. The design approach for UHPFRC structures are relatively similar to conventional concrete design. This paper presents the working example on the design of 70m span ultra-high-performance fibre reinforced concrete (UHPFRC) composite bridges. The working example mainly focus on (i) the material properties used in the structural analysis software – MIDAS CIVIL; (ii) the output results on the design forces at the critical sections (i.e. design moment effect, MEd and shear force effect, VEd); (iii) the stresses and midspan displacement of the post-tension UHPFRC U-girder at transfer and at different construction load historyand (iv) the design moment resistance (MRd) and design shear resistance (VRd) of the composite section.

Design shear resistance of headed studs embedded in solid slabs and encasements

This paper presents the results from reliability analyses on the design resistance of headed stud connectors embedded in solid concrete slabs and encasements. The present study substantially extends the earlier reliability work for Eurocode 4 by considering a database of 242 push tests, which permits the results presented to be considered valid over a wide range of characteristic compressive concrete strengths (8≤fck≤90MPa) and stud diameters (12.7≤d≤31.75mm). As well as considering the performance of the existing Eurocode 4 design model, two alternative design models were also studied. Although the design models for steel failure performed well, it was found that the current target value of γV=1.25 was not justified in the design models for concrete failure. In response to this finding, the design models were modified to ensure that the target value was delivered. In the interests of harmonization between the Eurocodes, further improvements were made to enable design equations to be proposed that deliver a uniform value for the partial factors, which may be considered worthy for inclusion within the second generation of Eurocode 4. Finally, from the significant number of tests considered in this paper, a revised procedure is presented for evaluating the characteristic resistance of stud connectors from small numbers of nominally identical push tests.

Experiment study on fatigue performance of perforated shear connectors

In order to investigate the fatigue behavior of perforated shear connection in steel-concrete composite bridges, 24 connection specimens with different geometric configurations were subjected to static and fatigue testing protocols. Using the design shear resistance of perforated shear connectors obtained from static push-out tests as a reference load level, numbers of fatigue cycles under different cyclic load levels were determined. Accumulated relative slip between steel and concrete components was used to characterize and track fatigue damage accumulation. The relationship between cycle numbers and accumulated relative slip between steel and concrete was established. Test results revealed that the fatigue damage of perforated shear connectors can be divided into three stages, and fatigue life of perforated shear connectors can be evaluated by the accumulated slip, which depends on the maximum shear stress and stress range.

Long-term design of FRP-PUR web-core sandwich structures in building construction

The structural behavior of GFRP-polyurethane (PUR) web-core sandwich structures subjected to sustained loading was investigated. As a basis, a study of the mechanical behavior of rigid PUR foams used as core materials was conducted, with emphasis on creep. The study showed that the foam anisotropy, its density and the loading type applied must be considered to assess the structural performance of the GFRP-PUR web-core sandwich. The influence of creep on the web-core interaction, i.e. on the shear load distribution and local instability phenomena were then analyzed. The effects of applying particular design recommendations on the design were assessed based on the example of a real GFRP-PUR sandwich roof. The design shear resistance of the GFRP webs, their dimensions and governing failure mode significantly depended on the applied recommendation. A design procedure to evaluate the overall shear resistance of the GFRP-PUR core over time, taking into account creep effects, was presented.

Shear resistance of concrete reinforced with ultra-high strength steel fibres

In order to evaluate the performance of high strength concrete reinforced with Dramix 5D 65/60 BG fibres, with non-deformable hook and ultra-high tensile strength, 24 beams were subjected to shear, with different fibre content (0, 15, 30 and 50kg/m3), with and without stirrups in the shear span. In a second test campaign, 18 of those beams were tested again in the opposite end, with a variable shear span/effective depth (a/d) ratio in order to evaluate the influence of this parameter in the shear crack pattern and shear resistance. A probabilistic approach was followed to derive the corresponding design value of the shear strength (a procedure herein named by Design Assisted by Testing, DAT), which was then compared with the design shear strength determined according to recommendations of RILEM, EHE and FIB. Test results of both campaigns showed a significant increase in shear strength in relation to beams without fibres. Besides that, the design values of the shear strength derived from test results (DAT) were considerably higher than the design shear resistance provided by design codes.

Analytical and numerical evaluation of the design shear resistance of reinforced concrete slabs

AbstractThe aim of this research is to compare the predictions of the design load‐carrying capacity of slabs obtained with simplified analytical and numerical procedures which can be readily used by analysts in the current design process. The research fits into a research programme initiated by the Dutch Ministry of Infrastructure and the Environment for the re‐examination of the load‐carrying capacity of existing bridges and viaducts, and the beams and slabs they include, through the use of non‐linear finite‐element analyses. The behaviour of reinforced concrete slabs subjected to concentrated loads close to their supports is investigated in this contribution. Three tests from a series of 18 slabs with a total of 108 tests, tested at Delft University of Technology, were selected as case studies and analysed with non‐linear finite‐element analyses and analytical models either proposed by design codes or available in the literature. The research agrees well with the philosophy of the fib Model Code for Concrete Structures 2010, which offers different analytical and numerical calculation methods for evaluating the design shear resistance of reinforced concrete members according to different levels of approximation. For the three slabs investigated in this study, it indeed pays to use higher levels of approximation. The highest level (level IV) based on non‐linear finite element analysis gives the highest design load resistance, but still well below the resistance obtained experimentally.

Shear resistance evaluation of prestressed concrete bridge beams: fib Model Code 2010 guidelines for level IV approximations

AbstractThe design shear resistance of an existing structure can be evaluated with analytical design procedures and numerical procedures provided by non‐linear finite element analyses. The new fib Model Code 2010 proposes different calculation methods that fall into four different levels of approximation. As the level of approximation rises, so the complexity and the accuracy of the calculated shear resistance increases. Non‐linear finite element analyses belong to the highest level of approximation, but although they are more and more becoming a customary tool in the daily design process, building codes do not provide guidance on how to perform these analyses.This paper describes non‐linear finite element analyses performed on prestressed beams, which underwent shear failure during experimental loading, in order to assess and criticize the finite element approaches. The aim of this work is to propose guidelines for numerical simulations in order to reduce model and user factors. The results obtained from the non‐linear finite element analyses have been compared with the analytical results using different levels of approximation. The design shear resistance obtained with the highest level of approximation, level IV, derived from non‐linear finite element analyses, turned out to be higher than the design shear resistance obtained with analytical procedures (levels I/II/III).

Discussion of "Strength Analysis of Steel-Concrete Composite Beams in Combined Bending and Shear"

In the paper, to assess the ultimate resistance of a simply supported composite beam, a three-dimensional beam element was used to model discrete stud shear connectors, and the studs were assumed to connect the middle plane of the concrete slab and the top steel flange of the steel beam both were modeled by shell element. This should be crucial in the finite-element study and raise a question how the shear connection stiffness in the analysis model was derived, which should not be the stiffness in real beam or that simply from push-out test. Accordingly, the full shear connection for a composite beam is known as being sufficient shear strength provided by the shear connectors in the critical shear span at the interface between the concrete slab and the steel beam to enable full plastic strength in the steel beam section. Let Pst be the design shear resistance of each stud; n be the available number of studs in the critical shear span; nf be the number of shear studs capable of being a full shear connection composite beam; and Fu be the ultimate longitudinal force resisted by the shear connectors. The required number of shear connectors within the critical shear span to enable full shear connection is determined as