Floor Joists Research Articles

An experimental study of cold-formed steel connections with screwed clip angle under tension and shear loads

This paper aims to investigate the performance of typical cold-formed steel (CFS) beam-to-beam connections between floor bearers and floor joists through a series of full-scale experiments. The investigated connections consisted of a lipped channel (floor joist), an unlipped channel (floor bearer), a thin-walled clip angle (connector), and a self-drilling screw (fastener). In this study, customised T-shaped and H-shaped CFS connection specimens were tested to examine the performance under tension and shear loads, respectively. Two sizes of self-drilling screws, 10 G and 14 G, were used with the selected load bearing clip angle. The fabricated connection specimens were subjected to displacement-controlled tension and shear loads. The experiments uncovered the ultimate connection strengths, load-displacement relationships, and failure mechanisms of the designed CFS connections under the applied loads. Moreover, the experimental tensile and shear strengths of the connections were compared with the strengths predicted by the standard design equations. It was found that the screw pullout on the anchored leg of the clip angle was the main mode of failure under the tensile load. On the other hand, two different failure modes—fracturing of 10 G screws or shear buckling of the cantilevered leg of the clip angle with 14 G screws—were observed in the H-shaped specimen under the applied shear load. Among the designed connection specimens, the maximum tensile load capacity was 30.86 kN and the maximum shear load capacity 88.15 kN. The standard design calculations predicted screw pullout failure under tension, while the shear bucking failure mode of the clip angle under shear load was overlooked.

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.

Web bearing design of cold-formed austenitic stainless steel un-lipped channels under localised interior loading

The high corrosion resistance, recyclability, ductility, and durability of stainless steels make them appealing for use in the construction industry. However, when used as structural channel sections, they are subject to localised failure in the web. This study aims to evaluate the structural behaviour of cold-formed austenitic stainless steel unlipped channels under localised interior loading. The results of conducting a novel testing programme with 21 new tests on such channels with different cross-section sizes and thicknesses are presented. Then a non-linear quasi-static Finite Element (FE) model is developed. The FE model is validated against experimental test results and found to demonstrate a good agreement in terms of bearing capacity and failure modes. It is found that no cold-formed stainless steel standard provides web bearing capacity equations for the localised interior loading (IL) that apply when simulating a floor joist on a solid foundation. The web bearing capacities are compared with capacities determined from the literature (including DSM). It is found that for the case of unlipped channels (unstiffened flanges), the current equations are unreliable and unconservative by up to 36%. The experimental investigation shows that, the American specification (SEI/ASCE 8:2002) is unconservative as much as 41%. Using both experimental and numerical results from this study, a new design equation is proposed for austenitic stainless steel unlipped channels under localised interior loading.

Application of multiple dynamic vibration absorbers in reducing low-frequency vibration of a floor-like lightweight joist structure: Comparison of experimental and computational results

Typical solutions to reduce excessive floor vibration and radiated sound to the room below include increasing floor mass, stiffening floor structure, and adding a floating floor in the source room. However, these methods may not be effective for lightweight floors at low frequencies. The use of dynamic vibration absorbers (DVAs) to reduce low-frequency structural vibration has attracted the attention of researchers in recent years. In this paper, an analytical model is proposed to study the effect of DVAs on the vibration of a lightweight joist structure by combining the bending modes of the plate with the bending and torsional modes of the beams. The analytical model is compared with the results from finite element models and measurements on a scaled wooden joist floor structure with fabricated spring-mass-type DVAs. A good consistency between the analytical results with results from the latter two are found in terms of the structural vibration and the DVAs’ effects.

E90 round-robin—Status and path forward

A good understanding of the uncertainty of a test method is necessary to interpret the results of said test. The ASTM E90 test has many potential sources of variation that can lead to significant uncertainty in the test results, but this uncertainty is not well documented in the precision and bias statement within ASTM E90. The current precision and bias statement provides some limited repeatability data for a wood joist floor and a concrete slab and only provides reproducibility data for the ASTM E1289 reference specimen. The E1289 reference specimens are simple steel plates in single and double-layer configurations that yield STC ratings far below those of the wall and floor/ceiling assemblies that are commonly tested. The authors are in charge of a new round-robin that aims to provide more detailed repeatability and reproducibility data using common wall designs with STC ratings in the range more commonly seen in building code requirements and design guidelines. In this presentation, the authors will cover their proposed plan for the round-robin and will give an update on its status.

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.

The forced sound transmission of finite periodic plates using a variational approach

Many engineering structures consist of plates being periodically stiffened or loaded. Examples can be wooden joist floors, dry walls with wooden or metal beams, or metamaterials for increased sound insulation. Even though some of these structures are well known and thoroughly studied in the past, there lack prediction models that can handle both the finiteness and periodicity in a simple and accurate manner. In two previous attempts, the periodicity of the structure have been tried to be incorporated in a variational technique based on integral-differential equations of the fluid loaded plate, based on [J. Brunskog, JASA 132, 1482-1493, 2012]. These attempts have not worked well: they show a poor fit with measured data. In this paper, this issue is investigated again, and a different tactics is used to incorporate the periodicity, using space harmonics. In this way, the paper try to explain the previous misfit and improve the model.

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.

Experimental Study and Numerical Simulation Analysis on Vertical Vibration Performances of 12 m Span Wood Truss Joist Floors

Walking-induced vibration control in wood floors is a critical issue attracting the attention of many researchers and engineers. This paper presents an experimental study applying static deflection tests, modal tests, and pedestrian load tests to a series of full-scale 12 m span tooth plates connected to wood truss joist floors with strongbacks and partition walls. A comparison of the calculation error of vibration parameters between the theoretical formula and a numerical model was also conducted. The results show that strongbacks and partition walls effectively reduce both the vertical displacement and the root means acceleration at the center of the floor under pedestrian load but increases the natural frequency. The partition wall can achieve a better vibration-reduction effect than strongbacks. The error of the finite element model is higher than that of the theoretical formula. Using the theoretical formula in engineering wood floor design is recommended.

New predictive equations for tilting and bearing resistance of U-shaped shear connectors in composite cold-formed steel floor joists using neural networks and stepwise regression

Due to the low thickness of cold-formed steel (CFS) sections, welding of traditional studs on them is not recommended; and there is a need to use shear connectors suitable for this type of sections. In this paper, the behavior of U-shaped shear connectors as connectors compatible with CFS composite beams has been investigated, to offer practical relationships for predicting the ultimate strength of this type of connectors. Accordingly, after the development of finite element (FE) models with the ability to predict the ultimate strength of U-shaped connectors, their performance against experimental results was validated. Then, an extensive parametric study, consisting of 216 numerical samples, was accomplished to provide a reliable database. As the main and most important of this study, two methods of artificial neural networks and stepwise regression were developed, and practical formulations were proposed to predict the ultimate strength of U-shaped shear connectors in CFS composite beams. Finally, in addition to evaluating the accuracy of the proposed formulas, a comparison was made between them and the relationships proposed by AISI, AS/NZS and EC3 codes for CFS screw connections. The relationships presented in this paper can be used by practical engineers in the design process of CFS composite beams.

FLEXURAL BEHAVIOR OF A BRACED HYBRID STEEL-TIMBER BEAM

A hybrid steel-timber beam commercially available in Australia is subject to a flexural test to study its mechanical performance. To mimic the practical use of the beam as a floor joist and reproduce the lateral restraints offered by the flooring, two beams were connected to each other using lateral bracing. The braced beam system was tested in four-point bending. The beams not only achieved their full loading capacity, but they also displayed excellent ductility, which could make them suitable for use in seismic prone areas. A finite element analysis of the tests is carried out to understand the performance of the beam and to validate the model so it can be used to carry virtual tests on different configurations of hybrid beams. The study revealed that if a hybrid steel beam is to display ductility, the steel web must be thin to fail first before the cracking of the timber.

EFFECTIVENESS VALIDATION ON EXISTING DESIGN EQUATIONS FOR THE SUSTAINABLE DESIGN OF MASONRY BUILDING RETROFITS

Due to the unsatisfactory performance of MS544-5 in estimating the design capacity of bolted timber connections, this present study was initiated to validate the existing predictive equations used by the Malaysian Standard (MS544-5). An evaluation of the European Yield Model (EYM) equation was also done to provide an optimal design equation for the bolted connection design in local hardwood. To verify these two sets of equations, a series of bolted timber connection tests was conducted on Nyatoh hardwood. Nyatoh was chosen as its strength makes it ideal for use as structural timbers, either as roof rafters or floor joists in masonry building constructions. The bolted timber connection tests conducted involved eight types of bolt configurations and the tests on each configuration was done in sets of 10 specimens. The experimental values obtained were then compared with the predictive equations of MS544-5 and EYM to examine their effectiveness. From the comparison, it was found that the prediction values given by MS544-5 were overly conservative with an average effective ratio of 0.34 while the EYM had an average effective ratio of 1.09. Thus, the use of EYM equations was recommended for the sustainable retrofit design development of Malaysian masonry buildings.

FLEXURAL BEHAVIOR OF A BRACED HYBRID STEEL-TIMBER BEAM

A hybrid steel-timber beam commercially available in Australia is subject to a flexural test to study its mechanical performance. To mimic the practical use of the beam as a floor joist and reproduce the lateral restraints offered by the flooring, two beams were connected to each other using lateral bracing. The braced beam system was tested in four-point bending. The beams not only achieved their full loading capacity, but they also displayed excellent ductility, which could make them suitable for use in seismic prone areas. A finite element analysis of the tests is carried out to understand the performance of the beam and to validate the model so it can be used to carry virtual tests on different configurations of hybrid beams. The study revealed that if a hybrid steel beam is to display ductility, the steel web must be thin to fail first before the cracking of the timber.

Optimal Design and Competitive Spans of Timber Floor Joists Based on Multi-Parametric MINLP Optimization.

This study investigates the optimization of the design of timber floor joists, taking into account the self-manufacturing costs and the discrete sizes of the structure. This non-linear and discrete class of optimization problem was solved with the multi-parametric mixed-integer non-linear programming (MINLP). An MINLP optimization model was developed. In the model, an accurate objective function of the material and labor costs of the structure was subjected to design, strength, vibration and deflection (in)equality constraints, defined according to Eurocode regulations. The optimal design of timber floor joists was investigated for different floor systems, different materials (sawn wood and glulam), different load sharing systems, different vertical imposed loads, different spans, and different alternatives of discrete cross-sections. For the above parameters, 380 individual MINLP optimizations were performed. Based on the results obtained, a recommended optimal design for timber floor joists was developed. Engineers can select from the recommendations the optimal design system for a given imposed load and span of the structure. Economically suitable spans for timber floor joists structures were found. The current knowledge of competitive spans for timber floor joists is extended based on cost optimization and Eurocode standards.

Unified approach for the web crippling design of cold-formed channels: Carbon steel, stainless steel and aluminium

Cold-Formed (CF) structural members have become important in conventional and emerging modular building constructions. However, point loads can result in web crippling failure of floor joists, purlins and decks. Due to their enhanced structural, aesthetic and resistive properties, CF aluminium and CF stainless-steel beams are used as an alternative solution to CF carbon steel beams. This paper ultimately investigates the web crippling behaviour of lipped channel beams under Interior Two-Flange (ITF) loading conditions. Since there is no unified approach is available for web crippling behaviour of various materials, this study focused on it. Three structural materials were considered as part of the study: carbon steel, aluminium and stainless-steel. Available experimental studies were used to validate Finite Element (FE) models, before an extensive parametric study (378 FE models) was carried out. Commercially available lipped channels with relatively lower web depth were considered to examine the web crippling behaviour under lower slenderness. Current design codes showed inaccurate prediction up to 15% against the results. This paper ultimately proposes new unified design guidelines for predicting the web crippling capacity of CF carbon steel, CF aluminium and CF stainless-steel lipped channel beams under ITF loading conditions.

Compressive loading of structural insulated panels and conventional stud walls: a study

Structural insulated panels (SIPs) are structural elements comprising a core of expanded polystyrene insulation sandwiched between two oriented strand boards. They can replace conventional joist floors and stud walls in low-rise residential construction. Three identical samples of full-scale SIP walls and stud walls were tested according to ASTM standards and experimental results for the specimens were obtained in terms of their ultimate load capacity and failure mechanism. Comparison of the load–deformation diagrams of the SIPs and stud walls showed that tangential stiffness variation of the former occurred in the hardening mode, whereas the variation for the latter was in two stages, hardening and softening. Regarding compressive loading, the results showed that SIPs are as good as conventional wood framing of the same size. Therefore, SIP walls are very efficient in the case of axial compressive loading.

Demonstration Project Reporting Detection of Subterranean Termite (Blattodea: Rhinotermitidae) Infestation and Spray Polyurethane Foam

Demonstration Project Reporting Detection of Subterranean Termite (Blattodea: Rhinotermitidae) Infestation and Spray Polyurethane Foam

Experimental Investigations and Numerical Simulations of the Vibrational Performance of Wood Truss Joist Floors with Strongbacks

This paper provides an experimental study and computer modeling analysis of vibration performance of full-scale wood truss joist floors, related to the static deflection and vibration mode/frequency and single-person-induced vibration. The vibration behavior of full-scale truss joist floors was investigated and the influences of the strongbacks on the vibration behavior were assessed. The results showed that the simulated predictions agreed well with the measured results. Strongbacks do not significantly affect the fundamental frequency of the truss joist floors but influence the second and third modal frequencies. The use of strongback rows at mid-span effectively decreased the maximum deformation of point loading at floor center. The effect of adding strongbacks at one-third of each span on decreasing maximum deformation at the floor center was minimal. The case of walking parallel to the joist produced higher acceleration response at the floor center than that of walking perpendicular to the joist. The closer the placements of strongbacks were to the mid-span, the more significant reduction of the vibration at floor center was. Two strongback rows at mid-span performed the best effect on reduction of vibration response at floor center. However, the use of strongbacks had limits of reduction peak acceleration of the sheathing between the joists. The study provides a valuable guide for future vibration serviceability study and design optimization of wood truss joist floors.

Associations of house characteristics with indoor dampness and measured moisture: Results from three New Zealand House Condition Surveys in 2005, 2010 and 2015

Associations between house characteristics and inspector-assessed subjective indoor dampness (yes/no) and measured floor and ceiling joist timber moisture were measured, using the 2005, 2010 and 2015 New Zealand House Condition Surveys, involving 1572 timber-framed houses. We conducted logistic (dampness) and linear regression (moisture) for each survey separately and mutually adjusted for other house characteristics (ventilation, insulation, subfloor defects, building envelope condition (BEC) defects, tenure, number of occupants), climate zone (latitude), rainfall and outdoor temperature. The odds of subjective damp increased with: more BEC defects (p for trend <0.001), with adjusted odds ratios (aORs) of 3.9–9.6 (p < 0.001) across surveys for houses with 4 or 5 (of 5) defects, compared with houses with ≤1 defect; more subfloor defects (p for trend <0.01 for 2010 and 2015 surveys); less ventilation (p for trend <0.05 for 2010 and 2015 surveys); less insulation (p for trend ≤0.05 for 2010); and increased occupancy (aORs 1.2–2.3, for ≥5 occupants compared to 1–2, not significant). Dampness was more common in rental houses (aORs 1.6 to 2.2, p < 0.05 in 2015). Floor joist moisture content was higher in houses with more subfloor (1.2%–1.9% increase per defect, p for trend ≤0.01) and BEC defects (1.5%–1.8% for houses with 4–5 defects, p < 0.001 for 2005 and 2015 surveys). In conclusion, subfloor and building envelope defects were associated with both inspector-assessed dampness and objectively measured moisture in floor joists. Less insulation, ventilation and higher occupancy were associated with increased subjective dampness but not with measured moisture.

An experimental study on structural performance of U-shaped shear connector in composite cold-formed steel floor joists

Since few studies have focused on the shear connectors in the composite cold-formed steel beams so far, this paper studies the behavior of the U-shaped shear connectors which can be used in the composite beams comprising cold-formed steel beam and concrete slab. Accordingly, ten full scale push-out tests were conducted to investigate the ultimate load, failure modes, ductility and stiffness of the U-shaped shear connectors. For this purpose, four types of shear connectors by different screw diameters and orientation of U-shaped shear connectors with respect to the direction of the load were considered; and utilized by two types of cold-formed steel beams with thickness of 1 and 2 mm. The results have shown that change of the screws’ diameter from 4.8 to 6.3 mm, leads to an increase of the ultimate load about 25% and 40% for 1 mm and 2 mm thick specimens, respectively. It is also concluded that transverse shear connectors have a better performance than longitudinal ones considering both ultimate load and ductility. The main observed failure mode of all specimens was tilting and bearing in shear connectors except for two specimens which was incorporated with pull-over mode. Moreover, ductility of the shear connectors was examined according to EC4 code. The results show that except for two specimens, the other U-shaped shear connectors used in this study can be accounted ductile.