Lap Length Research Articles

EXPERIMENTAL STUDY ON PULLOUT BEHAVIOR OF LAP SPLICE CONNECTIONS BETWEEN DOUBLE-STEEL-PLATE COMPOSITE WALLS AND RC RAFT FOUNDATION IN NUCLEAR ENGINEERING

Combining the advantages of steel and concrete, the double–steel-plate composite (DSC) structures exhibit the advantages of high bearing capacity, good seismic performance and durability, and convenient construction, and they have been increasingly used in nuclear engineering projects. The connection between DSC walls and reinforced concrete raft foundation is the key to make full use of the aforementioned advantages. Compared with the traditional embedding connection and anchoring connection, the lap splice connection can greatly improve the construction efficiency, which gains more and more attention. However, there is few research on such connection. Therefore, in this paper, four 1∶2 scaled lap splice connections between double-steel-plate composite wall and RC foundation are designed, and the static monotonic loading tests are carried out. Through the observation of bearing capacity, stiffness, crack pattern and strains of steel plate and rebar, the influences of the arrangement of lapped bars and tie bars on the mechanical performance of the connections are explored. The test results show that this kind of connection can achieve equal strength and shows satisfactory ductility. Transverse bars can control the crack development effectively and improve the integrity of the connection greatly; in addition, the tie bar strain along the lap length is not linearly distributed. The higher eccentricity of the lapped bars, which means larger unbalanced moment between the reinforcement and the steel plate, will result in lager strains of the transverse bars and lower slip of lapped bars. This paper provides experimental basis for the design of lap splice connections.

Experimental and numerical investigation into flexural bond strength of RC beams exposed to elevated temperature

The flexural bond strength of reinforced concrete beams exposed to elevated temperature has been investigated experimentally as well as numerically. The variables such as diameter of bar, lap or development length (Ld), concrete strength and thermal loading has been considered. The normal and high strength (NSC and HSC) RC beams of size 80 × 120 × 900 mm with different Ld provided at mid-span were cast and cured for 28 days. RC beams were then tested in flexure for bond strength after the single heating-cooling cycle of elevated temperature ranging from 200 °C to 800 °C at an interval of 200 °C corresponding to a heating rate of 5 °C/min. for 3 hrs heating duration. The cracks observed in most of the beams were propagating horizontally and were confined along the lap length due to lateral extension of bars causing bond loss when subjected to elevated temperatures. The NSC beams persisted up to 600 °C while HSC beams survived the thermal exposure up to 800 °C with some residual strength. It has been observed that the strength and stiffness of beams decrease with increase in temperature and decrease in lap length. It has also been observed that with decrease in the diameter of rebar result in increased bond strength, while the stiffness of the beam increased the ductility reduced as the diameter of the tension splice increased. Good agreement has been observed between the measured bond stresses and predicted bond stresses using the equations proposed by researchers and design codes. The numerical analysis of RC beams with different splicing length (Ld) has been successfully carried out using the finite element modelling. The numerical results showed an adequate estimate of the experimental results. Further, the numerical studies based on the finite element based model are extended for the parametric studies considering the lap length and the diameter of rebar as variable parameters.

Application of genetic algorithm in damage detection of reinforced concrete beams using piezo ceramic transducers

Health monitoring of reinforced concrete bridges and other large-scale civil infrastructures has received considerable attention in recent years. However, traditional inspection methods (x-ray, C-scan, etc) are expensive and sometimes in-effective for large-scale structures. Piezo-ceramic transducers have emerged as new tools for the health monitoring of large-scale structures due to their advantages of active sensing, low cost, quick response, availability in different shapes, and simplicity for implementation. This study presents an experimental effort for the detection of damages in the reinforcement bars at lap zone of the reinforced concrete beams using Piezo-ceramic Transducers (PZTs) with the help of Genetic Algorithm (GA). An Electromechanical admittance (EMA) approach is used to evaluate the damages in the RC beams for standard lap length provided in IS 456 code and optimized lap length of bars. Tests are performed in i) steel reinforced bars with standard lap length embedded in a reinforcing concrete beam of 1.3m span subjected to flexural load for detecting the response and damages ii) steel reinforcing bar with optimized lap length given to a reinforced concrete beam of span 1.3m subjected to flexural load for detecting the response of healthy state beam. Test measurements of healthy and damaged steel bars in the lap zone of the reinforced concrete beam have been conducted using the developed monitoring system and piezo ceramic transducers.

Behaviour of sandy soil reinforced with geotextile having partially and fully wrapped ends

The wraparound reinforcement technique has been studied recently by researchers as a way of improving the bearing capacity and load−settlement characteristics of a sand bed supporting a strip footing with a constant land width for foundation, but with the use of varying width of geotextile reinforcement. This research study presents an experimental evaluation of geotextile-reinforced sand bed enhanced with a wraparound reinforcement technique having partially and fully wrapped ends with the use of constant width of the geotextile reinforcement, but with varying land width of the foundation. Laboratory model tests were conducted to investigate the influence of the lap length coverage of wraparound ends on the load−settlement behaviour of reinforced sand. Additionally, an instrumentation programme with pressure cells was designed to study the pressure distribution in foundation sand beneath the geotextile layer. The test results reveal that fully wrapped models possess the most improved behaviour, with about 50% improvement in the bearing capacity and 50% reduction in the land width occupied by the reinforcement compared with a reinforced model without wraparound ends.

Optimal Design of Slit Impeller for Low Specific Speed Centrifugal Pump Based on Orthogonal Test

Marine centrifugal pumps are mostly used on board ship, for transferring liquid from one point to another. Based on the combination of orthogonal testing and numerical simulation, this paper optimizes the structure of a drainage trough for a typical low-specific speed centrifugal pump, determines the priority of the various geometric factors of the drainage trough on the pump performance, and obtains the optimal impeller drainage trough scheme. The influence of drainage tank structure on the internal flow of a low-specific speed centrifugal pump is also analyzed. First, based on the experimental validation of the initial model, it is determined that the numerical simulation method used in this paper is highly accurate in predicting the performance of low-specific speed centrifugal pumps. Secondly, based on the three factors and four levels of the impeller drainage trough in the orthogonal test, the orthogonal test plan is determined and the orthogonal test results are analyzed. This work found that slit diameter and slit width have a large impact on the performance of low-specific speed centrifugal pumps, while long and short vane lap lengths have less impact. Finally, we compared the internal flow distribution between the initial model and the optimized model, and found that the slit structure could effectively reduce the pressure difference between the suction side and the pressure side of the blade. By weakening the large-scale vortex in the flow path and reducing the hydraulic losses, the drainage trough impellers obtained based on orthogonal tests can significantly improve the hydraulic efficiency of low-specific speed centrifugal pumps.

Effect of Lap Length and Stiffness of Peel-Stop Fasteners in Single Lap Joints

Strength tests on single lap joints with one adhesive (AV138/HV998) and one adhesive layer thickness (0.5 mm), three peel stoppers (brass bolt, nylon bolt and steel pin), and four lap lengths (12.5 mm, 25 mm, 40 mm and 100 mm) were conducted to investigate the effects of varying the lap length and stiffness of the peel-stop fasteners. Joint failure stress decreased, but failure force increased with lap length. Furthermore, joint failure stress was higher with the peel stopper. The effect of the brass-bolt peel stoppers was significant, whereas the effects of the nylon bolts and steel pins were smaller than that of the brass bolts. This indicates that the axial clamp strength and stiffness of the peel stopper are important factors in the shear strength of the lap. In addition, the effect of the stopper was negligible for the 12.5 mm lap. The reason is that the shear strength in the case of the 12.5 mm lap was large and thus the effect of the peel stopper was comparatively small. Moreover, the strength of the 100 mm lap reached the adherent material’s strength.

Effect of adhesive layer properties on the shear strength of single-lap structures of dissimilar materials based on the cohesive zone model

An analysis method for improving the shear strength for the single-lap joints of dissimilar materials based on the cohesive zone model (CZM) is presented in this paper. The shear-lag model is established for the single-lap joint, and the stress distribution of joints is derived on the basis of this model, which is verified by simulation. The bilinear CZM is constructed to simulate the fracture process of joints, and the influence of lap length and adhesive layer thickness on the stress distribution of adhesive layers is comprehensively analyzed through simulation. Therefore, the effects of different properties of adhesive layers on the bonded structure strength are discussed with experiments. Results show that the reasonable lap length and thickness in this work are, respectively, 20–22 and 0.4–0.6 mm. The research results will serve as a guide for the parameter design, fracture prediction, and performance optimization of bonded joints.

The bearing capacity of monolithic composite beams with laminated slab throughout fire process

To investigate the failure form, bending stiffness, and residual bearing capacity of monolithic composite beams with laminated slab throughout the fire process, fire tests of four monolithic composite beams with laminated slab were performed under constant load and temperature increase. Different factors such as post-pouring layer thickness, lap length of the prefabricated bottom slab, and stud spacing were considered in the fire test. The test results demonstrate that, under the same fire time and external load, the post-pouring layer thickness and stud spacing are important parameters that affect the fire resistance of monolithic composite beams with laminated slab. Similarly, the post-pouring layer thickness and stud spacing are the predominant factors affecting the bending stiffness of monolithic composite beams with laminated slab after fire exposure. The failure forms of monolithic composite beams with laminated slab after the fire are approximately the same as those at room temperature. In both cases, the beams underwent bending failure. However, after exposure to the high-temperature fire, cracks appeared earlier in the monolithic composite beams with laminated slab, and both the residual bearing capacity and bending stiffness were reduced by varying degrees. In this test, the bending bearing capacity and ductility of monolithic composite beams with laminated slab after fire exposure were reduced by 23.3% and 55.4%, respectively, compared with those tested at room temperature. Calculation methods for the residual bearing capacity and bending stiffness of monolithic composite beams with laminated slab in and after the fire are proposed, which demonstrated good accuracy.

RETRACTED: Effect of different fibre types on the structural performance of recycled aggregate concrete beams with spliced bars

Abstract Providing a sufficient lap length to spliced bars plays a vital role to provide an adequate flexural strength and flexibility to reinforced concrete (RC) beams. This study intends to assess the influence of polypropylene fibres (PPF) and steel fibres (SF) on the flexural behaviour of recycled aggregate reinforced concrete (RARC) beams with spliced bars. For this purpose, 40 specimens with a cross-section 150 mm wide and 200 mm high, and a length of 1500 mm with different lap lengths in spliced bars, were cast and tested. One specimen was selected as a control beam with no fibres, recycled aggregate (RA) and spliced bars. Then, RA was replaced at 100% mass replacement ratio. Furthermore, to increase the cohesiveness between bars and concrete, which affect the flexural behaviour of RC beams, SF and PPF were added at 0%, 1% and 2% (by volume) separately. Four-point bending tests were performed to measure the load-bearing capability, ultimate deformation, flexibility and stiffness of RARC beams with different lap lengths. The influence of the fibres and of the lap length on the structural performance of RARC beams was the main aim of this investigation. Experiments indicated that the lap-spliced bars length could be reduced by 40% when both RA and 2% fibres are used with no reduction of the flexural strength of the beams, and the influence of 2% SF is higher than that of PPF.

Experimental study on interior precast concrete beam–column connections with lap-spliced steel bars in field-cast RPC

Reactive powder concrete (RPC) has an ultra-high bond strength with steel bars, which offers new and innovative opportunities for precast concrete structures. This experimental study aimed to develop an alternative precast interior beam–column connection for moment-resisting frames in seismic regions. A two-stage experimental program involved a series of lap-splice tests and two beam–column connection tests to assess the viability of lap-spliced steel bars in field-cast RPC (LS-RPC) used in a precast beam–column connection. In the first part of the study, the lap-splice tests were conducted to determine the minimum lap length of LS-RPC and the influences of embedment length, hoop ratio, and hoop type (rectangular or spiral). In the second part, the application of LS-RPC in the precast beam–column connection was performed to verify its reliability and its seismic performance with the expectation that this alternative precast interior beam–column connection for moment-resisting frames would be practical for application in seismic regions. It was determined that the application of highly ductile fiber-reinforced concrete in the potential plastic hinge zone could improve the seismic performance of the connection.

Effect of depth of epoxy coated lapped splices on bond efficiency

This paper gives a report of research investigation carried out to study the effect of depth of epoxy coated lapped spliced bars on bond strength and efficiency. Thirty-six full size beams of varying lengths and sectional dimensions with lap spliced bars in constant moment region were cast and tested in a four-point bending system. Bond strength and efficiency of epoxy coated top reinforcing bars were investigated using beams with 300 mm and 500 mm depths. Three beam sizes (300 × 180 mm, 300 × 200 mm and 300 × 230 mm) and high yield reinforcing bars (16 mm, 20 mm and 28 mm) were coated with epoxy over the lap length and used with each depth. The ultimate moments from the tests were used to determine the stress developed in the reinforcing bars. Coated top reinforcing bars were found to have lower bond strength and efficiency than coated bottom reinforcing bars in the depths investigated. The location factor, α, which is a reduction factor determined using an average of three beams, for epoxy coated top bars were found to be 0.86, 0.84 and 0.89 respectively for 16 mm, 20 mm and 28 mm diameter bars at 300 mm depth and 0.62, 0.80 and 0.86 respectively for 16 mm, 20 mm and 28 mm diameter bars at 500 mm depth.

Effects of key parameters on magnetic pulse welding of 5A02 tube and SS304 tube

The combination of collision velocity and angle plays a dominant role for the magnetic pulse welding (MPW) of dissimilar metals. During the MPW process of tubes, the combination depends on the key parameters including radial gap, relative lap length (RLL), and discharge voltage. In this work, the numerical simulations are performed to investigate the effects of RLL on the collision velocity and angle. MPW experiments of 5A02 aluminum tube and SS304 steel tube are conducted, and then, peeling tests and compression shear tests for the joints are carried out respectively to study the influence of these key parameters on the MPW joint quality. The simulation results reveal that the impact velocity declines with the enlargement of RLL but increases with the growth of radial gap and discharge voltage. And the collision angle decreases first sharply and then increases gently with the increase of RLL. And the angle also increases with the increasing radial gap but the discharge voltage seems to be less important. Comprehensively, it is found that there exists an optimum value 7/10 for RLL, 1.75 mm for the radial gap, and 16 kV for the discharge voltage to obtain the joints of good quality in this paper, whose shear strength’s maximum is up to 48.9 MPa. And the relationship between the radial gap and the voltage is found that the smaller the radial gap, the smaller the corresponding proper voltage for a good joint under the same experimental conditions.

Lap splices in confined self-compacting lightweight concrete

This paper presents an experimental investigation on the behaviour of spirally confined lap splices of deformed steel bar in self-compacting lightweight concrete (SCLWC). A total of twenty-four specimens were divided into three series and tested under tension. The difference among each series is the splicing details and configuration for each specimen. The parameters included to study the bond behaviour of SCLWC was bar diameter, lap length, and number of spirals. The experimental results include the ultimate load and bond stress along with cracking behaviour and failure mode of the specimens. A typical failure mode was observed for all specimens, which started after yielding of the steel bar. Proposed confinement details improved post-cracking behaviour and played a vital role in delaying and widening the cracks. The results showed that majority of the specimens achieved axial stress higher than the yield stress of the bar. The lap length for steel bars with diameter of 12 mm, 20 mm, and 25 mm can be used as short as 127 mm in confined SCLWC. In addition, the estimated development length based on different concrete design codes was compared with the experimental results. The results indicated that the codes included in the study have overestimated the development length and CSA-2014 code was the least conservative among all the other codes.

Bond behaviour of austenitic stainless steel reinforced concrete

Stainless steel reinforced concrete has seen a large increase in usage in recent years, in response to the ever-increasing demands for structures and infrastructure to be more durable, efficient and sustainable. Currently, existing design standards advise using the same design rules for stainless steel reinforced concrete as traditional carbon steel reinforced concrete, owing to a lack of alternative information. However, this is not based on test or performance data. As such, there is a real need to develop a full and fundamental understanding of the bond behaviour of stainless steel reinforced concrete, to achieve more sustainable and reliable design methods for reinforced concrete structures. This paper investigates the bond behavior of stainless steel reinforced concrete and compares the performance to traditional carbon steel reinforced concrete, through experimental testing and analysis. It also compares the results to existing design rules in terms of bond strength, anchorage length and lap length. It is shown that stainless steel rebar generally develops lower bond strength with the surrounding concrete compared with equivalent carbon steel reinforcement. Moreover, it is shown that existing design codes are very conservative and generally underestimate the actual bond strength by a significant margin. Therefore, following detailed analysis, it is concluded that current design rules can be safely applied for stainless steel rebar, although more accurate and efficient methods can be achieved. Hence, new design parameters are proposed reflecting the bond behaviour of stainless steel rebar, so that more efficient designs can be achieved. Moreover, a summary of recommendations for the codes of practice is provided.

Effect of over-ply on moisture absorption behavior of scarf-repaired composite laminate

The over-ply covering the bondline in scarf-repaired laminates can avoid direct exposure of the adhesive to moisture environment which would decrease the properties of the adhesive. The effect of the over-ply on moisture absorption behavior of scarf-repaired composite laminate was studied in this paper. 3D finite element models (FEMs) of scarf-repaired laminates with and without over-ply were established to simulate the moisture absorption behavior and verified by experimental results. Then these models were used to investigate the effects of some factors, including over-ply type, configuration, direction and number, on moisture absorption behavior of the repaired structures, especially of the adhesive. The results show that the over-ply can efficiently decelerate moisture absorption of the adhesive and delay the time of its moisture absorption equilibrium. Over-ply type has effect on moisture absorption of the adhesive. Woven over-ply is more effective to protect the adhesive in repaired laminates from moisture absorption than unidirectional over-ply. For the laminates with only large-circle bonding surface covered, over-ply lap length, configuration and direction are not very important parameters to affect the moisture absorption.

Experimental investigation for GFRP rebar couplers for reinforced concrete

The use of fiber reinforced polymer (FRP) rebars is nowadays becoming popular in reinforced concrete (RC) construction due to their excellent inherent properties such as corrosion resistance, lightweight, and high strength to weight ratio. The steel rebars, being susceptible to corrosion, are being replaced by FRP rebars. The higher strength of FRP rebars, as compared to steel, requires larger lap lengths when embedded in concrete. Although laps in steel rebars can be replaced by mechanical couplers, this is not feasible for FRP rebars. Thus, the present study investigates the use of couplers for Glass FRP (GFRP) rebars. Three types of couplers were tried: (i) steel pipe coupler, (ii) CFRP pipe coupler, and (iii) CFRP sheet coupler. These couplers were tested in direct tension for assessing their feasibility and establishing the design requirements. Although the steel pipe coupler demonstrated excellent performance, the use of CFRP pipe and CFRP sheet couplers were not successful. However, the performance of CFRP sheet couplers can be improved by increasing the length of sheet, and/or number of wraps.

Finite element analysis of strap lap bonding joints for wood powder/polyethylene composites with combined surface treatment

A design for strap lap bond joints of wood powder/polyethylene composites (WP/PE) was proposed. The effects of combined treatment on surface properties of WP/PE and failure modes of WP/PE bonded by epoxy and acrylic ester were investigated. A finite element model of strap lap bond joints of WP/PE was established based on the elastoplasticity finite element method, and the effects of lap length and adhesive (epoxy and acrylic ester) on stress distributions and comprehensive displacements of strap lap bond joints of WP/PE were investigated. The results demonstrated that the bonding interface roughness of WP/PE was enhanced by the combined surface treatment. Active oxygen-containing functional groups were introduced to the sample surface. The finite element simulation results revealed that the Mises equivalent stress peaks and comprehensive displacements of strap lap bond joints were concentrated in lap zone ends and board connections, the stress distribution was independent of the lap length, and the Mises equivalent stress peaks and comprehensive displacements were independent of the adhesive.

Multiscale Analysis on the Effect of Lap Length on Bonding Strength of Adhesively Bonding Structures of Plain Weave Composites

Multiscale Analysis on the Effect of Lap Length on Bonding Strength of Adhesively Bonding Structures of Plain Weave Composites

Mechanical Analysis of Grouted Sleeve Lapping Connector

Compared to grouted splice connectors that have been widely used in constructing precast concrete structures, grouted sleeve lapping connectors have the advantages of a large sleeve interior diameter and low manufacturing cost. In this study, 16 grouted sleeve lapping connectors and three grouted splice connectors were tested under an incremental tensile load. The differences in their tensile capacities and failure modes, especially the mechanical properties of the grouted sleeve lapping connectors, were investigated. It was found that the tensile capacities of the grouted sleeve lapping connectors were up to 2.45 times that of the grouted splice connectors when the sleeve inner surfaces were smooth. All of the grouted sleeve lapping connectors failed by a bar tensile fracture or bar-grout slip, whereas the only failure mode of the grouted splice connectors was grout-sleeve failure. The bond stress distribution around the inserted bar in the grouted sleeve lapping connector was similar to the bond stress distribution around a single bar anchored in concrete. The ultimate hoop compressive strain of the sleeve and the corresponding load increase with greater lap length. In addition, an approximate mechanical model with high reliability was put forward to describe the mechanical properties of the grouted sleeve lapping connector.

Behavior and Splice Length of Deformed Bars Lapping in Spirally Confined Grout-Filled Corrugated Duct

This paper discusses the behavior of grouted noncontact lap splices under monotonic tension load. Deformed bars lapped through a grout-filled corrugated duct, and a spiral reinforcement was preembedded in the connection to improve tensile strength of the splice. The experimental results show that bond failure splices are always failed by the pullout of the preembedded bar other than the grouted bar. As the spiral pitch distance is not greater than 75 mm, the tensile strength generally improves with the increment of volumetric spiral reinforcement ratio due to the higher confinement provided by the spiral bar. Compared with the spiral bar diameter, the spiral pitch distance provides more dominant effect on the tensile strength of the connection. Based on the experimental results and the development length specified in ACI 318-14, a revised equation with a reduction factor of 0.76 was proposed to predict the required minimum lap length of spirally confined lap splice.