Timber Joists Research Articles

Characterisation of timber joists-masonry connections in double-leaf cavity walls – Part 1: Experimental results

Post-earthquake structural damage shows that out-of-plane (OOP) wall collapse is one of the most common failure mechanisms in unreinforced masonry (URM) buildings. This issue is particularly critical in Groningen, a province located in the northern part of the Netherlands, where low-intensity induced earthquakes have become an uprising problem in recent years. The majority of buildings in this area are constructed using URM and were not designed to withstand earthquakes, as the area had never been affected by tectonic seismic activity before. OOP failure in URM structures often stems from poor connections between structural elements, resulting in insufficient restraint to the URM walls. Therefore, investigating the mechanical behaviour of these connections is of prime importance for mitigating damages and collapses in URM structures.This paper presents the results of an experimental campaign conducted on timber joist-masonry cavity wall connections. The specimens consisted of timber joists pocketed into masonry wallets. The campaign aimed at providing a better understanding and characterisation of the cyclic axial behaviour of these connections. Both as-built and strengthened conditions were considered, with different variations, including two tie distributions, two pre-compression levels, two different as-built connections, and one strengthening solution. The experimental findings underscored that incorporating retrofitting bars not only restores the system’s initial capacity but also guarantees deformation compatibility between the wall and the joist. This effectively enhances the overall deformation capacity and ductility of the timber joist-cavity wall system.

Analytical and experimental response of timber joists strengthened with an external underslung post-tensioned system

Floors made of timber load-bearing joists often do not meet modern load demands and strict code requirements. In pursuit of retrofitting such floors, this paper investigates the feasibility of strengthening timber joists with an external underslung post-tensioned system composed of a V-shaped tension chord and a midspan strut. An analytical approach is employed to assess the system’s response under live loads. Based on these findings, a short parametric study is used to identify the key parameters influencing the structural behaviour of the strengthened joists. To validate the theoretical results, an experimental programme is conducted on 9 full-scale specimens obtained from an existing XI-century building. The specimens were divided into three series based on a variable span-to-rise ratio of the underslung post-tensioned system. The experimental tests confirm the correct functioning of the system when applied to timber joists. Furthermore, the comparison between the analytical and experimental outcomes demonstrates consistent agreement across the various cases investigated, confirming the efficiency of the proposed system in increasing the load-carrying capacity of the timber joists. Specifically, the underslung post-tensioned system significantly enhances the load-carrying capacity of timber joists, increasing the flexural strength and stiffness up to 2.0-2.5 times and contributing to support up to 35% of the live loads.

Verification of a Simplified Design Method for Timber–Concrete Composite Structures with Metal Web Timber Joists

This study presents a comprehensive analysis of a simplified design methodology for timber–concrete composite roof and floor structures employing metal web beams, also known as posi-joisted beams, easi-joist, or open web joists, validated through both laboratory experiments and finite element (FE) method analyses. The proposed method integrates the transformed section method and the γ-method, as outlined in Annex B of EN1995-1-1 for mechanically jointed beams. The investigation focuses on roof and floor structures featuring posi-joisted beams, oriented strand board (OSB) sheets connected by screws, and a layer of concrete bonded to the OSB sheets using epoxy glue and granite chips. Two groups, each consisting of four specimens, were prepared for the laboratory experiments. Each specimen comprised two posi-joisted beams, 1390 mm long, connected by OSB/3 boards measuring 400 mm in width and 18 mm in thickness. The beams had a cross-sectional depth of 253 mm, corresponding to beams of grade PS10, with top and bottom chords made from solid timber (95 mm × 65 mm). Bracing members with cross-sections of 100 mm × 45 mm were used to join the bottom chords of the beams. A layer of self-levelling mass SakretBAM, 50 mm thick, was bonded to the OSB/3 boards using SicaDur 31 epoxy glue and granite chips (16–32 mm). The specimens underwent three-point bending tests under static loads, and FE modelling, conducted using Ansys R2 2022 software, was employed for both experimental groups. A comparative analysis of results obtained from the simplified design method, FE simulations, and experimental data revealed that the simplified method accurately predicted maximum vertical displacements of the roof fragment, including posi-joisted beams, with precision up to 11.6% and 23.10% in the presence and absence of a concrete layer, respectively. The deviation between normal stresses in the chords of the beams obtained through the simplified method and FE modelling was found to be 7.69%. These findings demonstrate the effectiveness and reliability of the proposed design methodology for timber–concrete composite roofs with posi-joisted beams.

Effect of wooden floorboards on the vibration of timber floor

This study is aimed at investigating those parameters related to timber flooring that can affect the acceptability of vibration behaviour of a timber floor in a residential building in view of the criteria stated in Eurocode EC5. The timber floor investigated is made of OSB/3 floorboards and timber joists. The parameters that are investigated in this study are thickness of flooring, floor joist span, joist spacing and connection of floorboards to the joists. In this context, two cases are considered. First: the flooring is nailed or screwed to the joists and no composite action or interaction is obtained between joists and floorboards. Second: the flooring is glued sufficiently to the joists and full interaction is obtained. The result suggests that glued floorboards perform much better with respect to natural frequency, static deflection and peak floor velocity than nailed or screwed floorboards. In almost all cases of glued floorboards, the result complies fully with the Eurocode 5 design vibration requirements. However, as floor lengths increase, the static deflection will increase beyond the allowable limit, especially for relatively thin floor panels and relatively widely spread joists. For both cases, increasing floorboards thickness and decreasing the joist span by adding more beams can yield even better results to satisfy the requirement of vibration comfort.

Walking test on Glulam-concrete composite floor

Glulam-concrete composite floor (GCC) is a hybrid flooring system which adopted from timber-concrete (TCC) flooring system concrete by replacing the sawn timber joist to Glulam timber joist. The concrete topping was poured on the concrete topping with stiffness connectors were installed to prevent the slip behaviour. Glulam timber is engineered timber that has a bigger strength compared to swan timber. This study is aims to identify the vibration behaviour of 7.6 m × 4.05 m Glulam Concrete Composite (GCC) floor. The walking tests were performed to get the vibration excitation on the floor. The person was walked horizontal and diagonal from one edge to another edge of the floor. The vibration data was recorded by accelerometer and analysis using ARTeMIS software package. The first natural frequency that obtained from both walking tests, (horizontally and diagonally walking test) were 12.9 Hz and 12.39 Hz, respectively. The natural frequencies were higher that 8 Hz as recommended by Eurocode 5, as acceptable value of limitation of vibration serviceability on the flooring system. As conclusion, the vibration behaviour of GCC floor was acceptable and the floor is comfortable to be used.

The influence of notch connection location on the short-term behaviour of timber-concrete composite beams, modelling of TCC beams and research for optimal locations, a numerical study

Timber-concrete composite beams, known as TCC beams, have been widely used in rehabilitation or in new buildings where several types of connections are commonly inserted to ensure partial composite action between the timber joist and the concrete slab. The notched connections represent an effective system due to their strength and ductility and it is simple to cut from timber joists. As a result, a small number is needed for the composite beam to achieve high performance in terms of bending stiffness and load-carrying capacity. This paper aims to develop a FE model for TCC beams with notched connections. It considers realistic interactions between different components. The developed FE model can satisfactorily predict the full range load-mid-span deflection curves and the failure mechanisms. The predictions agree very well with the experimental results reported in the literature, including the stiffness and the load-carrying capacity. After the validation, a numeric study was established, it aimed to research the optimal location of a notch connection between different proposed locations, to figure out which place must be installed to ensure high performance of the TCC beams. As a result of this study, the notch installed at location P3000 was found to be the optimal location to assure the highest bending stiffness. While the maximum carrying capacity was achieved at location P3750.

The sound of sustainable structures: Acoustic considerations for mass timber

The use of mass timber in multi-family and commercial buildings poses a range of challenges for acoustic designers, due in part to its recent emergence as a structural technology and relative light weight compared to concrete. The spectral performance of mass timber assemblies differs from that of concrete and of lightweight double-panel systems, such as timber joist floors, even when comparing assemblies with the same single-number airborne and impact sound transmission ratings. Due to the inclusion of mass toppings and damping layers, mass timber floor designs may outperform lightweight double-panel systems at low frequencies, but they are often challenged at mid to high frequencies, resulting in a sound spectrum that differs from established “acoustically acceptable” benchmarks. This study presents initial findings from listening sessions conducted in the Arup SoundLab, as well as various design strategies to balance performance, cost, aesthetics, and sustainability.

Low-frequency vibration of a timber joist floor section connected by metal screws: experimental validation of FEM models

The structural dynamics of a timber floor junction (six pieces of chipboard plate screwed to a single timber joist) have been investigated experimentally in a frequency range up to 200Hz. Experimental Modal Analysis (EMA), transfer mobilities and velocity level ratios between the chipboard walking surface and the joist were measured with 12 or 24 screw connections between the joist and the chipboard. These experimental data were used to validate Finite Element (FE) models that focussed on the interaction between the chipboard and the joist due to the screws. The aim is to develop validated FE models for timber floors that can be used to assess heavy impacts (such as the rubber ball impact source) and act as a reference for the future development of TSEA models for lightweight structures. The screws were modelled using both rigid connections and springs. For the latter, each point connection was modelled by four springs with stiffness (three coordinate directions and one rotational direction), with model updating using a Deep Neural Network (DNN). A comparison of mode frequencies and mode shapes from EMA and FEM will be made along with forced vibration of the structure.

An Investigation into the Strength Properties of Three Reclaimed Structural Timber Joist Within the University of Ibadan Community

Background and Objective: The investigation presents the results of selected test assessment on physico-mechanical properties of three selected wood residues within the University of Ibadan Campus, Oyo State, Nigeria. Often, reclaimed planks were considered as useful material for heating and energy production, hence, potential re-usability of these residues for plate rack production were determined. Materials and Methods: Four planks of the selected three wood samples each were collected from the University of Ibadan community. The 12 pieces wood samples were cleaned, plained, and converted into required dimension; samples were dried to about 12%moisture content before tests. Selected physico-mechanical properties test (moisture content, volumetric shrinkage, modulus of elasticity, and modulus of rupture were carried out according to ASTM standards. The data obtained were subjected to analysis of variance (ANOVA). Results: The results of mean density show that <i>Gliricidia sepium, Milicia excelsa </i>and <i>Funtumia elastica </i>had 1032±0.97kg/m³, 548±0.57kg/m³ and 613±0.33kg/m³, respectively. The mean value for moisture content of <i>G. sepium, M. excelsa and F. elastica</i> ranges from 12.47±1.21, 20.84±1.21 and 18.13±1.21, respectively. While, volumetric shrinkage of <i>G. sepium, M. excelsa and F. elastica </i>ranged from 20.55±2.79, 7.48±2.79 and 11.43±2.79. The <i>G. sepium, M. excelsa and F. elastica </i>had MOE values of 8793.13±643.43 N/mm², 8083.64±643.43 N/mm² and 4299.54±643.43N/mm². The mean values for MOR of <i>G. sepium, M. excelsa and F. elastica </i>ranges 404.69±12.362 N/mm², 434.27±12.36N/mm² and 388.34±12.36N/mm². Conclusion: <i>Gliricidia sepium </i>wood had the highest mean density, low shrinkage value and modulus of elasticity. Therefore, it was found most suitable wood slab for plate rack production from reclaimed wood joist.

Experimental and analytical study of timber-timber composite (TTC) beams subjected to long-term loads

Eight TTC beams were fabricated by connecting cross-laminated timber (CLT) slab panels to laminated veneer lumber (LVL) or glued laminated timber (GLT) joists and the TTC beams were subjected to a constant sustained load and monitored over 540 days in an indoor uncontrolled environment. Benchmark experimental data for validation of numerical and analytical models were produced and effect of joist type (LVL or GLT), CLT slab thickness (60 mm or 100 mm) and orientation (crosswise or lengthwise), and type and size of shear connectors (8- or 12-mm screws) on the long-term performance of the TTC beams were studied. The creep deformation factors obtained from experimental results were in the range of 0.39–0.73. Simplified analytical models available in the literature were modified and utilised to predict the mid-span deflections of the TTC beams. The midspan deflections predicted by the simplified models had good agreement with the test data. The inelastic strains due to (differential) shrinkage between the slabs and joists had minor (less than 3%) influence on the long-term deflections predicted by the models. The analytically estimated creep deformation factor for 50-year design life of the TTC floors was in the range of 0.55–1.26 that was slightly higher than the values obtained from the EC5 approach.

Numerical investigation for the flexural load behaviour of profiled composite slab strengthened with CFRP

The profiled composite slab (PCS) is a composite structural system consisting of profiled steel sheet in-filled with concrete in the troughs and connected using studs. This system is a structural load bearing element. Lately, this system has been increasingly used as flooring or roofing structural element. The PCS has become as an extension or development to the most popular now a day's composite slab called profiled steel sheet dry board which was brought to the United Kingdom as an alternative to timber joist flooring for small span domestically buildings. Similarly, to other structural members, PCS demands strengthening and continuous upgrading due to many reasons like exposing to accidents or to improve its ability to bear an extra load. There are a quite limited studies related to the improvement of the PCS strength thus, this study suggests investigating the effect of using carbon fiber reinforced polymer (CFRP) plates to strength the PCS and enhance its ability to carry an extra load. Three parametric studies were considered in this study, the effect of thickness, length and location of the CFRP plates on the flexural load behaviour. The FE analysis results, proved that using CFRP as a strengthen technique for the PCS system has a positive effect on the ultimate flexural bearing capacity which increased by 16.5%, 29.5% and 41.0% using different CFRP plate thickness (1.5, 3.0, and 4.5 mm, respectively). Moreover, when different CFRP plates length (1000, 1500 and 2000 mm) were used the ultimate flexural bearing capacity raised up to 4.0%, 10.0% and 16.5% respectively while the amount of increment were 16.5% and 39.0% when using different CFRP number of sheets (2 and 4 sheets respectively). Lastly, this study strongly recommends using CFRP sheets as a strengthen technique for the PCS system.

Advances in the Restoration of Buildings with LIDAR Technology and 3D Reconstruction: Forged and Vaults of the Refectory of Santo Domingo de Orihuela (16th Century)

This research presents a new intervention methodology on arches and vaults of a Renaissance factory in the Colegio Santo Domingo de Orihuela (16th century) using 3D software LIDAR technology that verifies the execution process of the works studying the different charges states and structure behavior. This document aims to explain a working methodology in the monitoring of structural repair interventions in the architectural heritage, in the specific case of the replacement of traditional one-way timber joist frame slabs on structures of former, splay and groin arches between vaults. This involves the compilation and processing of two types of data: on the one hand, the analysis of the different load states to which the intervention is exposed in its different phases: initial, dismantling of the different layers of traditional construction and replacement by the new structural system; and, on the other hand, the graphic information provided by the photogrammetry techniques used to dimension and define the spatial position of the structural elements that have historically resolved the covering of the architectural space in this type of Renaissance solution. The different layers and demolished materials have been verified by analysing their constructive disposition, thicknesses, and dimensions of the elements that formed part of the initial construction system and their own weights. In addition, the new construction systems used in the restoration project generate a state of loads similar to the existing one. The LIDAR technology used in the research process provides graphic data of the spatial position of the arches and vaults studied in the different states of the construction intervention. The point clouds obtained are analysed by taking as reference fixed points (considered unalterable and infinitely rigid) of the refectory and the coordinates of the initial and final states are compared. The results show minimal variations between the two positions, which justifies the goodness of the construction methods used and the structural safety obtained in the complex. This methodology applied to arches and vaults in heritage architecture guarantees the control and recording of the movements produced in the process.

Experimental and numerical study of long-term behaviour of timber-timber composite (TTC) connections

Long-term sustained load (push-out) tests under an indoor uncontrolled environment were conducted on twelve specimens (in seven groups/types) of Timber-timber composite (TTC) joints with up to two identical specimens of each TTC joint type. The TTC joints were fabricated by connecting either Laminated veneer lumber (LVL) or Glued laminated timber (GLT) joists to Cross laminated timber (CLT) slab panels. Types of joists (LVL and GLT), size of coach screw shear connectors, type of shear connection (screws with or without adhesive) between the joists and CLT slab thickness and orientation (i.e., lengthwise, or crosswise) with respect to the loading direction were the main variables in the experimental program. The laboratory tests revealed that the creep coefficient after 420 days is in the range of 1.05 to 3.90 and the CLT slab orientation has minor and CLT thickness has major influence on the creep coefficient of TTC joints (for a given service load over loading capacity ratio). A creep model was calibrated against the experimental slip-time curves and the model was used to predict the creep coefficient for the 50-year design life of the structure. It was shown that more than 50% of the creep in the TTC joints occur in the first year of loading. Additionally, a 3D coupled Finite element (FE) model implemented as user defined subroutines in ABAQUS/Standard was validated against the long-term test results and accordingly input parameters for coupled long-term FE analysis of the LVL-CLT and GLT-CLT joints (with screw shear connectors) are recommend. The validated FE model was used to further confirm effect of the CLT panel thickness and orientation on the long-term slip-time and creep coefficient of the TTC joints.

Analysis of the fire resistance of timber jack arch flooring systems used in historical buildings

Conservation of built heritage, at present, is a major task and a great challenge because it requires adapting the performance of existing buildings to current code requirements, when very often these were built before codes existed. Timber jack arch flooring systems can be found in many historical buildings around the world. The system is formed by timber joists and brick vaults spanning the distance between two adjacent joists and has an undoubtable aesthetic and cultural value. However, given its geometry, there is no methodology to verify its fire resistance, which has prevented the preservation of many buildings using this system. Within this context, this paper proposes a methodology based on the “Reduced cross-section method” included in Eurocode 5 (EN 1995-1-2) for the determination of the fire resistance of historical timber jack arch flooring systems subjected to different fire exposures. The methodology is based on the use of the 135-degree and the 300-degree isotherms to obtain the positions of the zero-strength layer and the charring depths, and is supported by both advanced numerical thermal models experimentally validated for standard fire exposure and advanced mechanical models. The methodology has been applied to a wide number of flooring systems covering different span lengths, timber static bending strengths, and fire exposures to evaluate the influence of these parameters on fire resistance. Results show that historical buildings do not always meet the requirements set by current codes and, therefore, performing these analyses is essential to ensure the fire resistance of these timber structures. By doing so, this work also contributes to cultural heritage conservation and to more sustainable construction in alignment with the fulfilment of United Nations 2030 Agenda’s eleventh goal: “Sustainable cities and communities”.

Strengthening of old timber floor joists with cross-laminated timber panels and tempered glass strips

This article deals with the procedure for strengthening existing timber floor joists with CLT panels and additional tempered glass strips. The proposed strengthening procedure was investigated on eight old timber floor joists from the historical Zgornja Polskava manor from Slovenia. The glass strips were adhesively bonded or screwed to the joists, while the CLT panels were screwed to the joists with self-tapping screws. The proposed procedure was evaluated based on four-point bending tests of the joists. The efficiency was determined by comparing the bending test results of the strengthened and unstrengthened joists. The bonded glass strip variant always resulted in a higher load-bearing capacity and a higher effective bending stiffness, while the screwed glass strip also always resulted in a higher effective bending stiffness, but only in some instances increased the load-bearing capacity. The experimental results were compared with analytical and numerical calculation results. The results showed good agreement, despite the joists being visually severely damaged, which was also demonstrated by performing acoustic tomography on a timber joist sample.

A Comparison on Numerical Simulation Models for Vibrational Performances of the Wood Truss Joist Floor System

Wood truss joist floors are increasingly used to replace traditional solid timber joist floors in low‐rise timber houses. An understanding of the vibration performance of wood truss joist floors is critical for the design and serviceability of the floors. It is difficult to model wood truss joist floors accurately because of the complicated boundary conditions and numerous sophisticated flexible connections. This paper discusses three simplified modeling methods for the wood truss joist floor system. The modeling results were validated by a series of static deflection tests and vibration modes and frequencies tests of a full‐size floor. And predictive analysis of human‐induced vibration of the floor was also conducted. The vibration characteristics of the wood truss joist floor were investigated. The examination of the applicability of these modeling methods was provided. The results indicate that the point loading deflection more easily affects the deflection of the adjacent joist. However, the deflection influence on other joists that are three spaces away is minimal. Walking on the wood truss joist floor produces steep vibration acceleration fluctuations at the floor center for a relatively long time period. The sheathing‐to‐joist connections and the metal plate connections of the joists have significant influences on the vibration response of the wood truss joist floor. The modeling method, which considers the flexible metal plate connections and flexible sheathing‐to‐joist connections, performs best for predicting the vibration performance of the floor.

Correlations between standardised and real impact sound sources in lightweight wooden structures

This study aimed to understand the correlation between standard impact sound sources and real impact sources in lightweight floor structures. Six real impact sources (adult walking, child running, child jumping on the floor, and three objects falling) were used to be compared with standard impact sources (i.e. tapping machine and impact ball). Measurements were conducted on a lightweight timber joist floor. Impact sound pressure levels (SPLs) produced by the standard impact sources were measured on the four floor structures with or without carpet tiles. For the real impact sources, two walkers wearing socks and slippers walked at different speeds (normal and fast) along three paths, while two children ran along the three paths and jumped at four positions. Also, the SPLs generated by dropped objects were measured at five positions. Seven standardised single-number quantities (SNQs) were calculated for the tapping machine and the impact ball, while three noise ratings (LAeq, LAFmax, and LN) were also computed from the sound recordings of the real impact sources. Both the tapping machine and the impact ball showed similar frequency characteristics with the real impact sources across all the floor structures. All the SNQs for the tapping machine and the impact ball were highly correlated with the energy-based noise ratings of the adult walking and little differences were found across walking speeds and footwear. Similar tendencies were observed from other real impact sources, indicating the high correlations between the standardised SNQs of the tapping machine and the impact ball and the noise ratings.

Erection of Formwork with Optimum Spacing of Joists and Stringers

The success of any project depends on suitable and economical formwork arrangements and it accounts about 25% in the overall cost. The project completion time depends on the erection and de-shuttering of formwork. Proper planning, management and safety is very important to finish the project within the cost budget and satisfactory quality. This study focuses on the conventional type of form work using timber joists and stringers loaded with different types of spacing in an actually erected model. The soil has been compacted, consolidated before the erection of model. After erections, the entire model has been subjected to sand bag loading with the specified loading capacity per sq. m. The deflections due to the added load on the formwork is characterized by standard deflectometer for different spacing of timber joists. Accordingly, the shores spacing have also been obtained with the designed load bearing capacity. With this study it has been found that the stability of formwork is analyzed based on vibrations and deflections. Hence the study infers that optimum spacing of joists designed should be decreased for minimum deflection. The vibrations and key factors for this erection have been identified and the results are presented.

Composite concrete – Unregularized timber section for flat roof construction

At a global level, there is a vital need to reduce the demand on concrete, because this construction material harms the environment, mainly due to carbon dioxide emission and destroying the surrounding nature for the purpose of taking raw materials during Portland cement manufacturing. This study is an encouraging attempt to utilize the natural resources for the roof construction and diminish using of concrete. This study aimed at investigating the structural behavior and performance of composite concrete-unregularized timber beam. The system essentially consists of a relatively thin concrete section slab and populus nigra timber (PNT) joist. Essential tests on concrete and timber materials were conducted in the laboratory, in addition to five composite concrete-timber beams. Results show that there is a good chance to use the PNT joist for composite roof construction. The resulted composite section is well recognized by a high stiffness and high load carrying capacity. It was found that steel screw fasteners provided at 100 mm spacing is the best arrangement and can be safely used for connecting concrete to the unregularaized timber section. Further, there is a chance to use Eurocode 5 design proposal to check the stresses in both materials safely at serviceability and ultimate limit stages, because the PNT timber behaves elastically till failure without appreciable post ultimate response.

TORSIONAL SHEAR STRENGTH PROPERTIES OF MALAYSIAN TROPICAL TIMBER IN STRUCTURAL SIZE

The shear strength of timber joists in timber design is important, especially to provide an adequate torsional stability and to avoid vibrational serviceability problems. In Malaysia, the data of shear strength of timber is available in MS544 Part 2. The data were developed by shear block test with small samples without defect known as small clear samples. Torsion test is one of the other approaches that can be used to attain the state of pure shear as it does produce a purer and a clearer shear stress distribution in the specimen, allowing measurement of the pure shear properties. However, in Malaysia, very little attention has been paid to the use of the torsion test in evaluating shear strength. Therefore, this study aims to investigate the torsional shear strength of selected Malaysian tropical timbers of different strength groupings (SG) namely Balau (SG1), Kempas (SG2), Kelat (SG3), Kapur (SG4), Resak (SG4), Keruing (SG5), Mengkulang (SG5), Light Red Meranti (SG6), and Geronggang (SG 7) using structural size timbers in accordance with BS:EN 408 and then compared with published by MS554: Part 2. The result shows contradictions of strength grouping between findings and published by MS554: Part 2. Resak (SG4) and Mengkulang (SG5) grade stress value have risen towards SG 3. Geronggang is currently in the SG6. Also from the findings, Kelat (SG3), Kapur (SG4) and Keruing (SG5) grade stresses are at par towards each other, even though they are completely in the different strength group as stated in MS544: Part 2. In conclusion, shear strength data need to be re-examined, since the strength for the tested specimen is much higher than the data given in MS 544 Part 2. This will lead to the increment in section and wastage in cost.