Half-lap Joints Research Articles

Toward Cost-Effective Timber Shell Structures through the Integration of Computational Design, Digital Fabrication, and Mechanical Integral ‘Half-Lap’ Joints

In a global context, where the construction industry is a major source of CO2 emissions and resource use, is dependent on concrete and its risks, and lags behind in digitalization, a clear need arises to direct architecture towards more practical, efficient, and sustainable practices. This research introduces an alternative technique for building timber space structures, aiming to expand its applications in areas with limited access to advanced technologies such as CNCs with more than five axes and industrial robotic arms. This involves reconfiguring economic and ecological constraints to maximize the structural and architectural advantages of these systems. The method develops a parametric tool that integrates computational design and manufacturing based on two-axis laser cutting for shells with segmented hexagonal plywood plates. It uses a modified ‘half-lap joint’ mechanical joint, also made of plywood and without additional fasteners, ensuring a precise and robust connection. The results demonstrate the compatibility of the geometry with two-axis CNC machines, which simplifies manufacturing and reduces the cuts required, thus increasing economic efficiency. The prototype, with a span of 1.5 m and composed of 63 plywood panels and 163 connectors, each 6 mm thick, supported a point load of 0.8 kN with a maximum displacement of 5 mm, weighing 15.1 kg. Assembly and disassembly, carried out by two students, took 5 h and 1.45 h, respectively, highlighting the practicality and accessibility of the method. In conclusion, the technique for building timber shells based on two-axis CNC is feasible and effective, proven by practical experimentation and finite element analysis.

Mechanical properties of glulam components with half-lap joints for large-span gridshell structures

Glulam gridshells provide a preferred structural form for large-span structures due to their aesthetic appearance and structural efficiency. As the gridshell span becomes large, the length challenge of glulam members associated with the manufacturing and transportation limits needs to be well addressed. Attention should also be paid to the influence of spliced joints on the structural performance of large-span glulam gridshell structures. This paper studies the effect of a type of commonly used half-lap spliced joints on mechanical properties of structural components for large-span glulam gridshell structures. Experimental tests were conducted on a series of full-scale intact and spliced glulam components. Two boundary conditions (i.e., roller and hinge supports) were employed in the tests, investigating the influence of axial compressive forces on the mechanical performance of glulam components. The failure modes, moment-rotation responses, moment capacities, rotational stiffnesses, and ductility factors of the specimens were compared. The test results showed that the moment capacity and the initial rotational stiffness of the roller-supported spliced specimens respectively reached 43.0% and 55.6% of the capacity and stiffness of the intact specimens. Compared to the roller-supported spliced specimens, the axial reaction force provided by the hinge support suppressed the initiation and growth of cracks within the tension zones of the spliced specimens, enabling them to fail in a more ductile manner. Analytical models were then developed to predict the moment capacity of glulam components with half-lap joints. The models were validated by the test results and can serve as a convenient tool for designing such joints.

Double-Sided Self-Pierce Riveting: Electro-Mechanical Analysis of Dissimilar Al-Cu Half-Lap Butt Joints

Double-sided self-pierce riveting (DSSPR) can be utilized as an alternative to self-pierce riveting (SPR) to produce butt joints through half-lap joints in dissimilar materials. The mechanical joining process makes use of tubular rivets with simple geometry that are here employed to join two sheets made from aluminium (Al) and copper (Cu). This research work analyses the influence of the stainless-steel rivet on both the electrical and mechanical performance of the joint. The electrical resistance variation of the joined assembly is measured at different temperatures and compared with conventional fastened joints made from the same material combination. The mechanical performance of the aluminium–copper connections is evaluated by means of shear tests and compared to the original fastened Al-Cu joint. An experimental approach is utilized to analyse the combined influence of different mechanical and electrical parameters to assess the performance of DSSPR in electrical applications.

Shear performance of tongue-and-groove joints for CLT

This paper presents an experimental study on tongue-and-groove (T&G) and half-lap (HL) joints for 5-layer cross-laminated timber (CLT) connected with self-tapping screws (STS). A total of 54 monotonic and cyclic loading tests were carried out for vertically screwed T&G and HL joints, the load-carrying capacity, stiffness, ductility, strength impairment and energy dissipation of the joints have been investigated. The results showed that the load-carrying capacity, stiffness and ductile ratio of T&G joints were higher than those of HL joints. Besides, joints with 8 mm diameter STS had higher load-carrying capacity, initial stiffness and ductility than those with 6 mm diameter STS. Fully-threaded (FT) STS could improve the loading-carrying capacity of the joints compared with partially-threaded (PT) STS, however, the stiffness and ductility were not as good as the latter. Under cyclic loading, the strength impairment rate of T&G joints was lower than that of HL joint, and the energy dissipation of T&G joints was better when the displacement was small. Two prediction models presented in this paper were conservative compared with the experimental values. The results presented in this paper can provide fundamental basis for supporting the potential engineering application of CLT panels connected with T&G joints.

Evaluation of Flexural Performance According to the Plywood Bonding Method of Ply-Lam CLT

The purpose of this study is to optimize the bonding method of the plywood suitable for cross-laminated timber (CLT) with plywood as a core by analyzing the flexural performance and failure mode according to the lamina species, the method of bonding plywood in the longitudinal direction, and whether or not adhesive is applied to the joint. In the case of the Douglas fir lamina layer, the modulus of elasticity decreased by about 11.5% due to longitudinal bonding, and the modulus of rupture increased or decreased according to the adhesive application and bonding method. The optimal conditions were derived as the butt joint without adhesive, half lap joint with adhesive, and butt joint. In the case of the larch lamina layer, the modulus of rupture and the modulus of elasticity decreased by about 15% and 40%, respectively. When using the half lab joint and tongue & groove joint, it is believed that it reduces the load transmitted to the middle layer by primarily preventing the failure on flexure at the joint of the plywood layer. From the results of this study, the larch lamina layer used in the manufacturing process of Ply-lam CLT did not show any difference based on the bonding method. Butt joint and half lap joint bonding method are determined to be suitable when using Douglas fir lamina layer.

Feasibility of the analytical model for the splice beam with half-lap joints reinforced with different cross-sections and layout of self-tapping screws

Experimental and theoretical works are reported to assess the mechanical properties of half-lap (HL) joint reinforced with self-tapping screws (STSs). An analytical model with high accuracy of calculation has been proposed for calculating the bending capacity of the splice beam with HL joint and STSs. However, the feasibility of the proposed model on predicting the bending capacity of a splice beam with different cross-sections and layout of STSs has not been thoroughly investigated. In this regard, the study aims at verifying the efficiency of the analytical model for the retrofitted splice beams with HL joints considering the effects of different configurations of STSs. Firstly, the flexural performance of the splice beams with different cross-sections and layout of STSs was compared with that of the intact beams. Secondly, the efficiency of the analytical model for such splice beams with different cross-sections and layout of STSs was calibrated based on the experimental results. Finally, the assumption used in calibration is validated by the test data. The results showed that the ratio of the 5th percentile value of the ultimate bending capacity of splice beams with HL to the 5th percentile value of intact beams has a significant increase compared with the previous study and reaches 75%. The calibrated analytical model for the splice beam with HL and STSs with different layout still possesses a high accuracy for the prediction of the connection capacity.

Distinctiveness of Welding Joints Design Based on Mechanical and Corrosion Environmental Influence on Low Carbon Steel

Experimental investigations were carried out to study the effect of weld joint designs and post weld heat treatment (PWHT) on mechanical and corrosion properties of low carbon steel. Butt, bevel and half-lap joints were produced with a voltage of 20 V and current of 110 A with the use of 3.2 mm diameter electrode E6013. Full annealing was carried out on part of the welded samples in order to consider the possibility of post weld heat treatment for better performance. The mechanical properties (tensile, hardness, and impact toughness) were studied for both the as welded (AW) and PWHT samples as well as the corrosion performance in a natural sea water environment containing 3.5 wt.% NaCl using potentiodynamic polarization method. The microstructure of the AW and PWHT samples of the welded joints with the most promising mechanical and corrosion properties were then characterized by means of an optical microscopy. The results obtained reveals that the bevel joint followed by half lap joint and the butt joint of the as weld samples gave the best combination of the mechanical properties considered. On the other hand, the corrosion properties of the butt joint were superior to that of the bevel and half lap joint, respectively in the PWHT condition as compared to the AW samples. This implies that PWHT improves the corrosion resistance of the welded steel joints.

Comparison of glulam beam-to-beam connections with round dovetail and half-lap joints reinforced with self-tapping screws

In this paper, the flexural performance of glulam beam-to-beam connections with two types of joint reinforced by self-tapping screws (STSs) was compared. 10 reference intact beams, 10 beams with half-lap (HL) joint reinforced by STSs and 10 beams with round dovetail (RD) joint reinforced with STSs were experimentally investigated under four-point loading. Experimental results of the tested specimens were presented in terms of failure mode, ultimate strength, moment/rotational angle relationship and ductility. The findings indicated that both the failure mode of the joints with HL and RD presented ductility to some extent, compared with the brittle failure of intact glulam beam. The results in terms of ultimate moment capacity were fitted with different distributions. The 5th percentile value of the capacity of HL joint and RD joint obtained from different distributions could reach 75.8–76.7% and 75.9–77.5% of that of the intact beams, respectively. In addition, the spliced beams with RD joint had a higher stiffness. Moreover, the average ductility ratio of the spliced beams with RD was 14% lower than the value of the spliced beams with HL. Furthermore, both of the HL spliced beams and RD spliced beams have significant lower variability compared to the intact beams which further facilitates the application of these joints.

Beech wood (Fagus sylvatica L.) flooring structures designed to increase the basketball bounce height

The present paper investigates the performance of eight different structures of beech wood (Fagus sylvatica L.) floorings designed for indoor basketball game court. Floorboard strips with the same lengths and widths and different thicknesses of 20 mm and 15 mm, respectively, were used to build the tested flooring structures. Joists and noggins with the same sizes and half lap jointed form the support construction mounted on the foundation. The same construction of sports floorings was applied to both categories of floorboard strips. Four variants of each category were tested. They were different through the material and position of the shock pads placed at the contact with the foundation. These variables were set in the experiment in order to improve the basketball bounce height. The tests were carried out according to SR EN 12235 standard. The best bounce heights were recorded for structures with floorboard strips of 20 mm thickness, provided with wooden shock pads placed at the half distance between the joists and noggins joints. For thinner floorboard strips, the rubber shock pads proved to be more efficient when positioned under the half-lap joints.

Fire resistance of unprotected cross-laminated timber (CLT) floor assemblies produced in the USA

Fire concerns are one reason for building code restrictions against tall wood buildings in US. Despite growing body of empirical data on fire performance of cross-laminated timber (CLT) generated in Europe and Canada, lack of full-scale tests performed on structural CLT “made in the USA” is often quoted as a barrier for approval of massive timber in tall buildings in the US. The goal of this project was to contribute towards removing this barrier by testing the fire resistance of three full-scale unprotected CLT floor assemblies fabricated by two US-based manufacturers. The assemblies represented two species groups (SPF and DF-L), and two adhesive systems (PUR and MF).All assemblies met ASTM E119 standard qualifying criteria for 2-h fire rating in loaded condition. While char fall-off was observed in assemblies bonded with PUR, the differences in mean char rates in the first two layers between assemblies bonded with PUR and MF were smaller than the variability of char rates within individual assemblies. Statistical significant difference was observed only for cumulative char rate for the entire time of exposure. The effect of softening of the PUR bonds was most apparent as an accelerated rate of assembly deflection in the late stage of the tests. The unprotected half-lap joints provided adequate barrier against transmission of hot gases and flames through the assemblies.

Impact of Selected Structural, Material and Exploitation Factors on Adhesive Joints Strength

Adhesive bonding is currently one of the most popular techniques of joining different materials. It is worth noting that this process is more and more often used in several industries: automotive, transport, mechanical engineering, medicine, electronics, light industry, as well as many others. The present article is aimed at determining an impact of selected structural, material and exploitation factors on adhesive bonds' strength. Strength tests were carried out on adhesive connections of pine wood. An exploitation factor under analysis was resistance to different temperature values - both positive and negative. Six different variants of a bonds' seasoning temperature value were used. Another variable factor was a structure of bonds, i.e. adhesive butt joints and adhesive half lap joints. Also, two types of adhesives were used: one of them was dedicated to wooden elements bonding, whereas the second one was a two-component adhesive composition based on epoxide resin. Strength tests described in the present article showed substantial impact of selected structural, material and exploitation factors on the adhesive bonds' strength.

Cross-laminated timber connections assembled with a combination of screws in withdrawal and screws in shear

The research presented in this paper examines the performance of 3-ply cross-laminated timber (CLT) panels connected with self-tapping screws (STS). Half-lap joints with STS loaded in either shear or withdrawal along with an innovative solution combining these two approaches were evaluated in a total of 24 quasi-static monotonic and 15 reversed cyclic tests. The CLT joint performance was evaluated in terms of load-carrying capacity, yield strength, deformation capacity, stiffness, and ductility. The results demonstrated that joints with STS loaded in shear exhibit high ductility but low stiffness, whereas joints with STS in withdrawal are very stiff but brittle. Combining STS that act in shear with STS that act in withdrawal can lead to connections with high stiffness and high ductility. The performance of STS shear connections under reversed cyclic loading is comparable to that of these connections under quasi-static loading; however, all performance values are reduced by up to 40% demonstrating the necessity to provide designers and engineers with connection performance data under cyclic loading for reliable seismic design.

Numerical modelling of the cyclic behavior of timber-framed structures

The present paper presents a study on the applicability of numerical models in predicting the global response of timber-framed shear walls during earthquake events. Based on previous in-plane cyclic testing of traditional timber frames with and without masonry infill, numerical models were developed to describe the cyclic response of traditional timber frame walls including flexural behavior, pinching and strength degradation. The numerical models were developed in the finite element software OpenSees with calibrated springs representing nailed connectors found in traditional half lap joints. Based on the calibrated models a study was conducted on the timber frame wall with brick infill model by varying wall configuration and analysing cumulative energy dissipation and the effect of slenderness and load capacity with increasing drift. A good correspondence was obtained with the experimental data and future work will include the application of the model to whole buildings.

Mechanical Properties of Furniture Self-locking Frame Joints

The load carrying capacity, stiffness, and strain fields of 18 mm thick and half lap 30 mm thick L-shaped furniture self-locking frame joints made of a Finnish birch plywood and a birch battenboard were determined. The joints were tested under tensile and compression bending. On the basis of the experimental information, finite element analysis models were verified. The data showed that the joints made of birch plywood reached a higher load carrying capacity and stiffness than the joints made of the birch battenboard with the same thickness. The Half lap joint (H L J) made of the Finnish plywood reached the ultimate load carrying capacity and the ultimate stiffness under both the compression bending and the tensile bending. The finite element analysis models of the joints can be used for estimating the mechanical properties of the self-locking joints with different tenon shapes made of the materials used in this paper.

Performance evaluation of traditional timber joints under cyclic loading and their influence on the seismic response of timber frame structures

Timber joints represent the governing part of a timber structure, particularly when assessing its seismic response. In order to better assess the seismic capacity of traditional timber frame structures, particularly timber-framed shear walls, pull-out and in-plane cyclic tests were carried out on their joints (half-lap joints). The aim is to better understand the influence of the joints on the walls and their influence on failure mechanisms and capacity.Their seismic characterisation was obtained via the analysis of the hysteretic behaviour and dissipative capacity of both unreinforced and retrofitted joints (using self-tapping screws, steel plates and GFRP sheets).Results show that all strengthening techniques were able to improve the dissipative and load-bearing capacity, but care should be taken into not over-stiffening the joints, as it would lead to an overly rigid structure.

靱性型木造面格子壁を用いた耐震シェルターの基本構造特性の把握

A number of wooden houses have been destroyed under earthquake. From a structural viewpoint, the authors developed simplified seismic shelter which is consisting of timber grid wall with half-lap joint. The concept of this shelter is saving securing space even if housing is collapsed. Although the stiffness of this shelter is smaller than the conventional grid shear wall for seismic retrofit, this shelter has ability of ductile and energy absorption by embedding at a joint. In this paper, these basic characteristics are verified by experiments and numerical analysis.

Steel Bar를 이용한 리기다소나무 목재옹벽의 내력 평가

Pitch pine (Pinus rigida Miller) retaining walls using Steel bar, of which the constructability and strength performance are good at the construction site, were manufactured and their strength properties were evaluated. The wooden retaining wall using Steel bar was piled into four stories stretcher and three stories header, which is 770 mm high, 2,890 mm length and 782 mm width. Retaining wall was made by inserting stretchers into Steel bar after making 18 mm diameter of holes at top and bottom stretcher, and then stacking other stretchers and headers which have a slit of 66 mm depth and 18 mm width. The strength properties of retaining walls were investigated by horizontal loading test, and the deformation of structure by image processing (AlCON 3D OPA-PRO system). Joint (Type-A) made with a single long stretcher and two headers, and joint (Type-B) made with two short stretchers connected with half lap joint and two headers were in the retaining wall using Steel bar. The compressive shear strength of joint was tested. Three replicates were used in each test. In horizontal loading test the strength was 1.6 times stronger in wooden retaining wall using Steel bar than in wooden retaining wall using square timber. The timber and joints were not fractured in the test. When testing compressive shear strength, the maximum load of type-A and Type-B was 130.13 kN and 130.6 kN, respectively. Constructability and strength were better in the wooden retaining wall using Steel bar than in wooden retaining wall using square timber.

리기다 소나무 정각재를 사용한 목재옹벽의 직결나사못 접합부 내력 성능 평가

시험 시편은 1개의 횡목과 2개의 종목이 직결나사못 2개로 연결된 접합부(Type-A)와 2개의 횡목과 2개의 종목이 4개의 직결나사못으로 연결된 접합부(Type-B)를 제작하였다. Type-B를 보강하기 위하여 횡목간의 연결부를 끝면거리 5D로 반턱이음하여 2개의 직결나사를 사용한 접합부(Type-C), 끝면거리 10D로 반턱이음한 접합부(Type-C1)와 끝면거리 10D, 직결나사 3개를 사용한 접합부(Type-C2)를 제작하였다. 압축형 전단 내력 시험결과 Type-B의 내력을 기준으로 Type-B를 보완한 Type-C는 약 30% 감소하였고, Type-C에서 끝면거리를 증가시킨 Type-C1은 Type-B와 비슷한 내력을 보였으며, Type-C1에서 직결나사못의 개수를 3개로 증가시킨 Type-C2는 Type-C1과 비교하여 1.28배 내력을 나타냈다. 기존 정각재를 이용한 옹벽의 접합부 중 긴 횡목과 짧은 횡목이 2개의 종목과 연결되는 접합부는 내력이 저하되기 때문에 이를 대체하기 위하여 실험을 실시하였다. 따라서 Type-B를 Type-C2로 대체한다면 옹벽 시공시 직결나사못에 의한 목재의 할렬, 파단과 시공시간이 줄어들고 접합 내력이 증가할 것으로 기대된다. A connection was made between a single stretcher and 2 headers with 2 threaded nails (Type-A), and another one between 2 stretchers and 2 headers with 4 threaded nails (Type-B) to use as specimens. Type-C was the stretchers that are connected with 2 threaded nails by half lap joint at end-distance 5D to reinforce Type-B, Type-C1 the stretchers that are connected by half lap joint at end-distance 10D, and Type-C2 with 3 threaded nails at end-distance 10D. Compressive shear strength of Type-C, the supplementation of Type-B, was decreased by 30%, compared with that of Type-B. Those of Type-B and Type-C1 that used longer end-distance than Type-C were about the same, and that of Type-C2 connected with 3 threaded nails was 1.28-times stronger than that of Type-C1. Connection of the retaining wall using existing square timber has a problem between long and short stretchers and 2 headers. So it was investigated in the experiment to replace it. Therefore, if Type-B is replaced with Type-C2 in constructing the retaining wall, the crack and the rupture of timber caused by threaded nail as well as construction period can be reduced, and also it can be expected to increase their own strength.