Shear Provisions Research Articles

Shear Reinforcement of Existing Reinforced Concrete Beam Using Deep Embedment Method

The load capacity of old reinforced concrete structures must be increased to meet current standards. This might be due to increased load needs, inadequate shear provisions in the original design, material degradation, or rising demands for shear capacity related to flexural strengthening. This research demonstrates a method that effectively repairs RC beams using embedded steel bars. Loading history was reproduced in the form of cracking within the elastic range in 2000 x 150 x 200 mm beam. The beam was repaired and then reloaded to failure in the experimental test. The results show that the contribution of steel bars embedded in the core of the RC beam to the load capacity can be significant. The highest initial stiffness of the strengthened beam was 13,07 kN/mm, which was 69% higher than the control beam, while the maximum load of the strengthened beam was 43 kN with the deflection at 13,00 mm, 43% higher than the control beam. The cracks developed during the reinforced beam’s second load phase were identical to the first, and the shear capacity increased more than the control beam.

Experimental investigation of punching shear behaviour of ultra-high performance self-compacting concrete slabs

The use of heavy reinforced and thick transfer-slab in multipurpose tall buildings is crucial to dealing with many issues such as high bending and punching shear stresses created from relocation of columns in floors above transfer-slab. Ultra-High Performance Self-Compacting Concrete (UHPSCC) is a proper option for coping with the problem of dense reinforcement. In predicting the punching shear capacity of concrete slabs, most existing code provisions limited the concrete compressive strength up to 70 MPa. Furthermore, no code provisions deal with estimating the punching shear capability of UHPSCC slabs. For these reasons, the present paper aims to investigate experimentally the punching shear behaviour of the interior slab-column joint made of a developed UHPSCC blend had a compressive strength of more than 120 MPa. The study takes into account the effect of design parameters such as type of concrete, slab thickness, and reinforcement ratio on the punching shear capacity. The study explores if the existing code shear provisions could be utilized to estimate the punching shear strength of UHPSCC and UHPC slab-column connections. In terms of estimating the punching shear capacity of such slab-column joints using available code provisions, regardless of their concrete compressive strength limits (using the available code formulae to estimate punching shear strength twice, once with the code restrictions of concrete compressive strength and once without), the available code shear models were significantly conservative, indicating the need to develop a new punching shear model for such slab-column connections. The European Code (EC2, 2004) has the best appropriate formula for predicting the nominal punching load capacity of UHSC slabs among the present well-known code punching provisions. The critical punching section of the UHPSCC slab was detected at 1.5 times the slab's effective depth measured from the column face. For a slab thickness of 200 mm, increasing the tensile steel ratio from 1.3% to 2.0% increased the punching strength of UHPSCC by 77.6%. At a reinforcement ratio of 1.7%, raising the slab thickness from 160 to 240 mm boosted the punching strength by 118.6%. In view of the study's outcomes, in addition to its ability to address the issue of dense reinforcement, the use of UHPSCC provides great potential for improving the punching shear capacity of heavy-loaded slab-column connections.

Model uncertainties and partial safety factors of strain-based approaches for structural concrete: Example of punching shear

The development of mechanical models relating the state of strains and the resistance of reinforced concrete structures has become a trend in the last decades. These types of models are referred to as strain-based approaches. Since strain-based approaches usually involve multiple sub-models and take implicit forms, their model uncertainties tend to be more complex than those of the explicit design equations commonly used in design codes. The characteristics of the model uncertainties of strain-based approaches is investigated using the Critical Shear Crack Theory (CSCT) for the punching shear resistance of structural concrete members as example. Both by performing theoretical parametric analyses and by evaluating relevant experimental data, it is shown that the model uncertainty of global resistance solution of strain-based approach can be viewed as resultant of the model uncertainties of the sub-models. In addition, it is also shown that the model uncertainty of the global resistance solution can be lower than those of the sub-models, depending on their sensitivity relationship. The model uncertainties of different Levels-of-Approximation (LoA) of the CSCT for punching are also compared. The LoA approach intends to provide consistent and progressively refined model for different design tasks in practice. The model uncertainty quantification result confirms that the model uncertainty of higher LoA of CSCT has lower variability and also less conservative bias than lower LoA. Finally, based on the obtained model uncertainties, different types of partial safety formats for strain-based approaches are compared and discussed. Using the CSCT punching shear model as an example, it is shown that the partial factors applied to the sub-models are more suitable for higher LoAs since they can effectively account for the change of model uncertainty associated to the change of failure mode. Based on the assumptions described in this work, the relationship between the partial factors of the punching shear provisions in the 2nd generation of Eurocode 2 for the design of new structures and the assessment of existing critical ones is established.

Modification of Approximate Method of ACI 318 Prestressed Concrete Shear Provision

Modification of Approximate Method of ACI 318 Prestressed Concrete Shear Provision

Analisis Elemen Hingga Terhadap Perilaku Balok Beton Bertulang Yang Diperkuat Dengan Menggunakan Metode Deep Embedment

Bridges are infrastructure buildings that are affected by technological developments. Beam structures on bridges often experience a decrease in strength, one of which is shear strength. Sometimes the shear capacity of reinforced concrete beam structures cannot meet the requirements at this time. This can be caused by increased loads, inadequate shear provisions in the initial design and material damage due to natural factors. Reinforcement methods by means of externally bonded (EB) and near-surfaced mounted (NSM) are methods that have been carried out to overcome the decrease in shear strength in beam structures. Shear reinforcement using the EB and NSM methods in practice only relies on epoxy bonding and concrete covers, this makes it susceptible to structural failure. Reinforcement method deep embedment (DE) can be used as a suggestion as shear reinforcement in reinforced concrete beams to overcome the previous problems. Reinforcement using the DE method is shear reinforcement which is reinforced at the core of reinforced concrete beams. The aim of this research is to analyzq the behaviour of reinforced concrete beams resulting from finite element modelling using ABAQUS software. This research was carried out by embedding 20 bars vertically with a distance of 100 mm along the shear span. The results of finite element modelling with ABAQUS software show that the maximum load obtained is 28,12 kN and the maximum deflection that occurs is 14,10 mm. The final result of the beam failure model is flexural failure. This is indicated by the initial crack pattern that occurs vertically in the middle of the beam span. The crack continues to propagate towards the compression area of the beam until the beam collapses.

Influence of openings on the punching shear behaviour of concrete slabs supported on special-shaped columns

Punching shear of special-shaped columns supporting reinforced concrete two-way slabs has been addressed in design codes since the late 1970s. While these provisions have existed for over 40 years their basis is unclear as previous studies related to the punching shear behaviour of irregular column geometries, such as L, T, and cruciform shapes, are limited. In this paper, the punching shear behaviour of L, T and cruciform slab-column connections, with or without slab openings near the connection, under concentric vertical loading is studied using a three-dimensional nonlinear finite element model (FEM) implemented in Abaqus/Explicit. The nonlinear FEM, based on the concrete damaged plasticity model, is used to study the influence of both the opening size and location on the punching shear behaviour of special-shaped (irregular) slab-column connections of various sizes. Based on the FEA results, the ideal location for openings around special-shaped slab-column connections (SS-SCCs) is between the column flanges. This location minimizes their negative influence on concentric punching capacity and is also beneficial architecturally. Finally, the accuracy of the ACI 318–19 punching shear provisions is evaluated. Based on the FEA results modifications to the existing provisions are necessary, particularly to account for the location of openings around special-shaped slab-column connections.

A mechanical approach for the punching shear provisions in the second generation of Eurocode 2

The revision of a code is a long-term project that shall fulfil several aims, comprising the enhancement of the ease-of-use and incorporating updated state-of-the-art. With respect to the revision of Eurocode 2 concerning the punching shear provisions, this task allowed also for the opportunity to enhance the understanding of the code and physical phenomenon by designers. The original EN1992-1-1:2004 punching provisions were adapted from an empirical equation for design based on the regression analyses performed by Zsutty in the 1960s for shear in beams and later reworked in Model Code 1990 for punching shear. These expressions did not show any link to the physical response of a structure, making difficult to designers to clearly understand how to engineer their designs. Instead of continuing with this approach, CEN/TC250/WG1 took the decision in 2016 to ground the punching provisions on a mechanical model that could be explained to engineers, allowing for a transparent understanding of the design equations and phenomena. To that aim, the Critical Shear Crack Theory, already implemented in Model code 2010 at that time, was selected as representative of the state-of-the-art. Following that decision, a large effort has been performed to implement this theory into the Eurocode, keeping its simplicity of use and generality. This paper is aimed at presenting the theoretical ground of the theory as well as the manner in which it is drafted for the future generation of Eurocode 2.

FRP Stay-in-Place Formworks for High Performance of Concrete Slabs

Stay-in-Place (SiP) formworks obviate the transportation, placement, removal and storage requirements of conventional formworks. Fibre Reinforced Polymer SiPs (FRP-SiP) have additional advantages, such as corrosion resistance, high specific strength and durability. This paper discusses an experimental instigation consisting of two sets of slabs having varying span-to-depth ratios cast on an FRP-SiP. Control specimens with conventional steel bar reinforcements were also cast. Several treatments for improving interfacial bonds at the interface between concrete and FRP-SiP have been investigated. Cyclic flexural tests were performed to evaluate their structural performance. Load-displacement relationship and load capacity are presented. Failure envelopes and energy absorption capacity were evaluated. It was found that the load capacity of FRP-SiP was around 107% greater than the conventional steel rebar specimens. Bond treatment on the FRP-SiP specimens increased the load capacity by around 215% over the untreated specimens. The load-deflection behaviour and the failure modes of the FRP-SiP specimens were distinctly different from those of the conventional specimens. The flexure and shear provisions in American Concrete Institute Standards (ACI 440) were found to be conservative in comparison to the present results. This study demonstrates that FRP-SiPs improve both the structural performance and construction efficiency of concrete slabs, however, new standards would be necessary to be able to utilize their improved capacity.

Enhanced Reliability Method for the Two-Way Shear Provisions of the European Code for Lightweight Concrete

The two-way shear failure of concrete elements is sudden; thus, reliable design codes are a must. In this current study, three reliability methods were implemented, namely: the Mean Value First Order Second Moment (MVFOSM), the First-Order Second Moment Method (FOSM), and the Rackwitez-Fiessler procedure (RFHL-FOSM) on the two-way shear provisions of the European design code for lightweight concrete. A brief state-of-the-art review of existing reliability methods is presented and compared. An extensive experimental database of lightweight concrete slabs testing under two-way shear loading was gathered. The reliability index was calculated for the design code. This index was compared with the target values set by international standards. For two-way shear of lightweight concrete, the European design code was found to achieve the target of reliability. The MVFOSM was found to provide a better reliability index than using the FOSM.

Shear strength of lightweight and normal-weight concrete slender beams and slabs: An appraisal of design codes

Lightweight concrete (LC) is a viable alternative for conventional normal weight concrete (NC). It has a reduced weight and similar properties. However, shear provisions design codes are way behind for the case of the LC compared to the NC. This study evaluates the shear design of NC and LC specimens. First, an extensive experimental database of these specimens under shear was compiled. Then, selected shear provisions of design codes were outlined and applied for strength calculations. The calculated strengths were evaluated considering the experimentally measured ones to assess these design codes' overall accuracy and consistency. In addition, the effect of selected parameters (depth, concrete strength, flexure reinforcement ratio, shear span to depth ratio, and nominal maximum aggregate size) on the safety of the design was assessed. The third draft of the Eurocode was the most accurate and consistent for the shear design of LC and NC specimens. Finally, the Eurocode shear provisions draft was adapted, refined, verified, and proposed for the shear design of LC beams and slabs.

Assessment of shear strength of reinforced concrete beams without shear reinforcement: A comparative study between codes of practice and artificial neural network

Despite 70 years of investigations in understanding the shear behaviour of reinforced concrete members, it is again gaining attention among structural engineers as the recently issued Australian concrete design standard, AS 3600 updated its shear provisions and ACI 318 unveiled its new one-way shear design equation. This study investigates the shear design equations in ACI 318–19 and AS 3600–2018 highlighting their strengths and weaknesses. A detailed parametric study is performed on a database of 1237 shear tests of point loaded RC slender beams without shear reinforcement. An Artificial neural network (ANN) was built, trained and validated with a subset of this database. Further, a very few experimental tests were conducted isolating the effect of a single variable on the shear failure load of RC beams without shear reinforcement. Thus, an ANN is an effective tool to investigate the influence of each variable individually. This study concludes that the introduction of size effect and ρw1/3 terms into the new ACI 318–19 code have resulted in greater accuracy compared to ACI 318–14 which it replaced. The study further demonstrates that AS 3600–2018 agrees well with all ranges of test parameters. The ANN demonstrated more accurate predictions compared to the codes of practice within the range of input parameters considered.

Block Shear Strength of Coped Beam Connections with Double Bolt Lines

AbstractCoped beam connections are commonly used in the construction of steel structures. Existing block shear provisions for these connections, with multiple bolt lines, account for the presence o...

Evaluation of design equations for out-of-plane shear strength of deep concrete sections in nuclear power plant buildings

Reinforced concrete walls in nuclear power plant buildings, which are generally more than one-meter thick, are typically designed to resist out-of-plane shearing force using concrete resistance only, namely, through-thickness shear reinforcement is not provided. Standard ASCE 43, which addresses design of safety-related nuclear facilities in the United States, references ACI 349 for design of reinforced concrete nuclear structures and components, with exceptions as deemed necessary. The code ACI 349–13, assumes, identically to ACI 318–08 and ACI 318–14, that the nominal shear stress capacity of longitudinally reinforced concrete sections is independent of cross-section depth: an assumption not supported by data. In the last revision cycle of ASCE 43, the ACI 349–13 design equation for concrete shear stress capacity was evaluated for conformance with the performance target of the standard, namely, a 98% or higher probability of exceedance, and found to be inadequate. A correction to the ACI 349–13 equation was developed and implemented in ASCE 43–19 to account for the effects of effective depth and longitudinal reinforcement ratio on concrete shear stress capacity. In parallel with the revision of shear provisions in ASCE 43, a size-effect modification factor, λs, was introduced in ACI 318–19 to account for the reduction in concrete shear stress capacity with increasing effective depth. In this paper, the technical basis for the correction factor included in ASCE 43–19 is developed and the ACI 318–19 equation is assessed to judge whether it achieves the ASCE 43 performance target. The assessment utilized the test data of longitudinally reinforced beams assembled by Reineck and his co-workers for slender sections (ratio of shear span-to-effective depth greater than or equal to 2.4) and non-slender sections (ratio of shear span-to-effective depth less than 2.4). For slender sections, the probability of exceedance of the ASCE 43–19 (ACI 318–19) design strength is greater than 98% (99%). For non-slender sections, the exceedance probabilities are greater than 99%. Because the ACI 318–19 equation meets the ASCE 43 performance target for both slender and non-slender sections, the correction invoked in ASCE 43–19 could be retired once ACI 349 adopts the shear provisions of ACI 318–19 for longitudinally reinforced concrete.

Effect of orientation of stirrups in combination with shear span to depth ratio on shear capacity of RC beams

The shear behavior of reinforced concrete (RC) beams has been a major research area for a long time. Since the shear response of RC beams is affected by different factors, many researchers have reported that the nature of shear behavior is complicated. One of these factors worth investigating is the inclination of shear reinforcements. This paper investigated the effect of the orientation of stirrups on the shear capacity of RC beams as the shear-span-to-depth ratio (a/d) varies. The contribution of concrete compressive strength was also studied. An experimental program investigating 21 RC beams has been conducted. The test results revealed that the shear capacity increases as the arrangement of stirrup changes from conventional vertical arrangement to inclined arrangement. However, the increment is high in beams with (a/d) ratio of 2.2 than beams with (a/d) ratio of 2.6, which are relatively slender. Shear capacity also increases as concrete compressive strength increase, which shows that concrete contribution to the shear capacity of beams should be taken in to account.In addition to the experimental test, the beams were analyzed numerically by using a general-purpose finite element package, Abaqus. The shear capacity of reinforced concrete beams obtained from the numerical analysis is in a good agreement with the experimental result. The results obtained by numerical analysis and experimental tests are compared to analytically calculated values by using shear provisions of ACI 318-14 and EN-2. Both ACI 318-14 and EN-2 are generally conservative in predicting the shear capacity of RC beams. However, the conservativeness of these codes reduced as a/d ratio of the beams increase.

Block shear strength in thin-walled lean duplex stainless steel fillet welded connection with base metal fracture

This paper investigates the accuracy of different design equations given in design specifications and literatures in determining the block shear strength of the lean duplex stainless steel fillet welded connections with base metal fracture. It points out the problem inherent in the block shear provision specified in the North American cold-formed design specification, which does not consider shear strain hardening. The previous test results have found that full shear strain hardening can be assumed for the carbon steel and ferritic stainless steel welded connections, but not applicable to the thin-walled lean duplex stainless steel welded connections with a higher ratio of the tensile strength to yield stress. Based on the results of finite element analysis including ductile damage simulation, this study reveals that the block shear strength of the lean duplex stainless steel specimens can be determined accurately using the mean between the shear yield stress and the shear ultimate stress. This paper also investigates the effect of stress triaxiality incorporated in the block shear equations found in the literature through comparative analysis with the bolted connection. The effect is shown to be negligible for the thin-walled lean duplex stainless steel welded connection, although higher stress triaxiality is developed in welded connection than in bolted connection. This paper recommends a block shear equation assuming the normal tensile stress in the net area in conjunction with partial shear strain hardening. The recommended equation was found to be more accurate than other equations for determining the block shear strength of the thin-walled lean duplex stainless steel welded connections.

Prediction of Shear Strength of Reinforced Recycled Aggregate Concrete Beams without Stirrups

For decades, recycled coarse aggregate (RCA) has been used to make recycled aggregate concrete (RAC). Numerous studies have compared the mechanical properties and durability of recycled aggregate concrete (RAC) to those of natural aggregate concrete (NAC). However, test results on the shear strength of reinforced recycled aggregate concrete beams are still limited and sometimes contradictory. Shear failure is generally brittle and must be prevented. This article studies experimentally and analytically the shear strength of reinforced RAC beams without stirrups. Eight RAC beams and two controlled NAC beams were tested under the four-point flexural test with the shear span-to-effective depth ratio (a/d) of 3.10. The main parameters investigated were the replacement percentage of RCA (0%, 25%, 50%, 75%, and 100%) and longitudinal reinforcement ratio (ρw) of 1.16% and 1.81%. It was found that the normalized shear stresses of RAC beams with ρw = 1.81% at all levels of replacement percentage were quite similar to those of the NAC counterparts. Moreover, the normalized shear stress of the beam with 100% RCA and ρw = 1.16% was only 6% lower than that of the NAC beam. A database of 128 RAC beams without shear reinforcement from literature was analyzed to evaluate the accuracy of the ACI 318-19 shear provisions in predicting the shear strength of the beams. For an RCA replacement ratio of between 50% and 100%, it was proposed to apply a reduction factor of 0.75 to the current ACI code equation to account for the physical variations of RCA, such as replacement percentage, RCA source and quality, density, amount of residual mortar, and physical irregularity.

A comparative study on minimum shear reinforcement provisions in codes of practice for reinforced concrete beams

The Australian Concrete Code (AS 3600) went through a number of significant changes to the shear provisions in the last decade through the introduction of the modified compression field theory. However, there were some discrepancies identified, specially related to the minimum shear reinforcement provisions. This paper investigates the parameters which affect the reserve strength of shear reinforcement using a database of shear tests of beams with minimum shear reinforcement. The current minimum shear reinforcement provisions in Australian concrete code (AS 3600-2018), Australian bridge design code (AS 5100-2017) and American concrete institute code (ACI 318-19) were reviewed using a database of 1237 shear tests of beams without shear reinforcement. According to the requirements for providing shear reinforcement, AS 3600-2018 demonstrated 50 % lower safety margin compared to ACI 318-19 and AS 5100-2017. Thus, in recent amendment 2 of the AS 3600 (released for public discussion) proposed a secondary factor, ks, to increase the safety of the requirement of shear reinforcement. In this study, effectiveness of the ks factor and an author defined constant factor, 0.75 were evaluated against the shear tests database. The conclusions based on the statistical analysis confirms that 0.75 factor is more efficient in increasing the safety margin compared to the ks factor.

One-Way Shear Strength of FRP–Reinforced Concrete Members Without Stirrups: Design Provision Review

Abstract The American Concrete Institute recently updated their one-way shear provisions for steel–reinforced concrete (RC), and it is time to consider updating provisions for one-way shear in fibe...

Shear strength evaluation in the existance of axial compressive loads for reinforced concrete beams

ABSTRACT Response-2000 is a program developed to calculate the shear capacities of beams and columns under any combinations of shear, moment, and axial loads. It is based on the modified compression field theory. The capabilities of the program Response-2000 to obtain shear strength capacities in the existence of axial compressive loads are demonstrated. The comparison with the experimental tests proved that the program gives good estimate for the failure shear in this case. The shear provisions of the Egyptian reinforced concrete code (ECP203-2017) are also evaluated against the experimental results. It is found that the accuracy of the obtained results using Rseponse-2000 is better than those obtained using the shear equations of the Egyptian reinforced concrete code (ECP203-2017). The program Response-2000 is then used to generate 336 results for 7 different cross-sections considering different concrete compressive strengths, transverse reinforcement, and values of axial loads. These generated results along with 33 experimental results for other 7 cross-sections are used to develop a new formula for the shear strength capacity in the existence of axial compressive loads. This formula is found to give better results when verified against experimental data.

Investigating ACI 318-08 Punching Shear Provisions for Design of Isolated Footings (Dept.C)

This study is concerned with investigating the punching shear provisions of ACI 318-08 with emphasis on Equation (11-32) of this code. For reinforced concrete slabs and footings, shear force resisted by concrete is taken as the smallest value evaluated from ACI Equations (11-31), (11-32) and (11-33). Based on the experience of the author in designing isolated footings, it is noticed that Equation (11-32) has never yielded the smallest shear capacity in isolated footing design, thus making this equation redundant in terms of punching shear design. In this work, Equation (11-32) is to be investigated theoretically and parametrically to prove its redundancy in terms of practical design of isolated footings