Steel Timber Research Articles

Steel–Timber Composite Beam-to-Column Connections with Shear Tab

AbstractThis paper focuses on the structural behavior and negative bending moment capacity of steel–timber composite (STC) beam-to-column connections with shear tabs. It is hypothesized that timber...

Seismic reliability analysis of a timber steel hybrid system

Seismic reliability analyses account for the inherent uncertainties in both the actions (earthquakes) and the reactions (properties of the structural systems) of a structure. To predict the failure probability of a structure, the system response due to external loads is usually estimated by a numerical method. In this paper, seismic reliability analyses were performed on a novel timber-steel hybrid system labelled FFTT (Finding the Forest Through the Trees) system. The FFTT system utilizes mass-timber panels to resist gravity and lateral loads and interconnecting steel members to provide the necessary ductility for seismic demands. To reduce the computational effort for reliability analyses, Genetic Algorithms (GA) and Analysis of Variance in combination with response surface methods were applied and compared. Uncertainties involving ground motions, seismic weight, connection properties of the lateral load resisting system, and ductility factor were considered in formulating the performance functions. Mean and standard deviation of peak inter-storey drift were selected as performance criteria. Nonlinear dynamic analyses were run to generate the response database for the FFTT system and the reliability index was calculated using second-order reliability methods. The results showed that the GA method was superior and that the ground motion was the most significant factor for structural reliability, while the ductility factor, the structural weight, the hold-down and connection stiffness also played significant roles.

Determination of Initial Stiffness of Timber–Steel Composite (TSC) Beams Based on Experiment and Simulation Modeling

Due to improvements in the use of recyclable materials in construction, timber–steel composite (TSC) beams demonstrate high potential for future construction. In this study, a proposed simulation modeling, which was adopted from the simulation modeling of a timber I-shape composite, was applied to estimate the initial stiffness of TSC beams. The strength of each beam could be determined once the initial stiffness was estimated. In addition, a series of experiments were performed to examine the accuracy of the proposed simulation modeling, including the effects of different shapes of steel members, fasteners, and applying and not applying a dowel connection. The results indicated that the simulation modeling could adequately determine strength at a deflection of 1/360 of the span. The ratio of difference between the experimental results and the simulation modeling results was less than 10% if a dowel connection at the web was applied. However, the ratio of difference reached 26% and 24% in the TSC beams without a dowel connection at the web that were fastened with screws and nails at the flange, respectively, revealing the importance of applying a dowel connection at the web. Moreover, the strength of the TSC beams with a dowel connection at the web that were fastened by screws was approximately 15% higher than that of TSC beams without screw fasteners. In conclusion, the proposed simulation modeling can provide designers with a method for estimating the initial stiffness and strength of TSC beams within a deflection of 1/360 of the span, supporting the future application of TSC beams in construction.

Seismic performance of embedded steel beam connection in cross-laminated timber panels for tall-wood hybrid system

Recent developments in novel engineered mass timber products and connection systems have created the possibility to design and construct tall timber-based buildings. This research presents the experiments conducted on the steel-wood connection as main energy dissipating part of a novel steel–timber hybrid system labelled Finding the Forest Through the Trees (FFTT). The performance was investigated using quasi-static monotonic and reversed cyclic tests. The influence of different steel beam profiles (wide flange I-sections and hollow rectangular sections) and the embedment approaches (partial and full embedment) was investigated. The test results demonstrated that appropriate connection layouts can lead to the desired failure mechanism while avoiding excessive crushing of the mass timber panels. The research can serve as a precursor for developing design guidelines for the FFTT system as an option for tall wood-hybrid building systems in seismic regions.

The Influence of Dowel-Bearing Strength in Designing Timber Pegged Timber Joints

ABSTRACTThe employment of timber pegs in timber structure joints is a widespread technology in the field of timber frame building in the United States, where the Timber Frame Engineering Council has published a special Standard to supplement the National Design Specification for Wood Construction. The authors have been studying the possibility of supplementing the Eurocode 5 design formulas, thought for timber joints with metal connectors, with specifications needed for a reliable design when employing timber pegs. The field of application envisaged is that of restoring timber structures and results obtained until now are quite encouraging. In this step of the research, more attention has been paid to deformation process: fir and chestnut samples have been tested to determine their dowel-bearing behavior with steel and ash timber peg while double-shear plane joints made of the same wood species, and fastened with steel as well as timber pegs, have been analyzed.

Connections for steel–timber hybrid prefabricated buildings. Part I: Experimental tests

Steel–timber hybrid construction systems, in particular structures with steel frames, composite steel–timber floors and shear walls with Cross-Laminated Timber (CLT) sheets, combine the industrialized construction technology typical of steel systems with the advantages offered by CLT panels, namely lightness and in-plane stability. The paper proposes some original engineered solutions for joining CLT panels with steel elements. Specifically, it examines connections which allow both prefabrication of the components in the factory and their quick assembly on site. Experimental tests performed on a number of different connections will be presented and discussed. The first Part of the paper addresses some fundamental aspects and potentialities of steel–timber hybrid prefabricated systems. Two innovative steel–timber hybrid components to build floors and shear walls will be described in detail in the companion paper (Part II).

Connections for steel–timber hybrid prefabricated buildings. Part II: Innovative modular structures

This paper aims at the development of multi-storey prefabricated modular buildings. Particularly, this document deals with a novel versatile construction system in which the main structural members, made by combining timber with steel, are highly engineered and can be produced in the factory. The research demonstrates the potential of steel–timber hybrid structures in terms of sustainability, providing lightweight modern seismic-resistant constructions. This document presents the results of a comprehensive experimental campaign, including tests on several innovative connections, and of the numerical FEM analyses of the structural components. The paper also provides prototypes of new highly-industrialized steel–timber hybrid shear wall and floor components.

Numerical damage prediction in dowel connections of wooden structures

The behaviour of timber connections is very complex because of the interaction between brittle and ductile failure modes that develop within the contact areas between the timber and the dowel. Simulating this behaviour numerically requires the use of multidimensional failure criteria as well as the use of coupled constitutive equations accounting for both non-linear isotropic hardening and isotropic ductile damage. Such a formulation is proposed in the present work and implemented within a Vumat user-defined subroutine in Abaqus/Explicit. The model is used to simulate the behaviour of a double shear timber steel connection. Good agreement was found between the FE results and experimental ones, which showed the good capability of the model to predict the onset of ductile damage and growth. It was found that failure results from ductile defects initiation, growth and propagation inside narrow shear bands wherein the plastic strain is highly localised.

Ductility Estimation for a Novel Timber–Steel Hybrid System

AbstractIn current force-based seismic design procedures, structures are allowed to behave inelastically during significant seismic events. For this reason, the applied design base shear of a structure is calculated by reducing the elastic strength demand by a ductility factor that represents the ability of a structure or structural system to deform inelastically beyond yielding. Whereas North American building codes provide ductility factors for traditional structural systems, including timber-based or steel-based systems, there are currently no design provisions available for novel hybrid structural systems. Thus research is required to define the force reduction factors, and specifically the ductility factor, Rd, to safely and efficiently design novel systems within the existing seismic design provisions. One such novel system is the so-called finding the forest through the trees (FFTT), proposed in 2012, where mass-timber panels act as shear walls and are connected to each other and to perimeter frame...

Timber Steel Fiber–Reinforced Concrete Floor Slabs in Fire: Experimental and Numerical Modeling

Timber–concrete composite floors represent an efficient possibility for strengthening timber beam ceilings and stiffening timber frame structures. The results of this construction method are higher stiffness and load bearing capacity, improved sound insulation, and better fire resistance. Replacing conventional RC with an innovative and efficient material, such as fiber RC, leads to improvements in the construction progress, material properties, and load transfer and to a reduction in the slab thickness. The subject of this paper is the numerical simulation of the behavior of composite timber-fiber concrete floor, consisting of a fiber concrete slab and timber beams. The primary point of this work is to explore the membrane action of the fiber concrete slab with timber beams and investigate the behavior of the load floor structure by using finite-element (FE) models. This paper presents a three-dimensional FE model developed to predict the mechanical behavior of timber-fiber concrete composite floors, to derive simpler models for representing the partially protected composite floors in fire. The analysis of these structures is nonlinear and considers the orthotropic behavior for timber and isotropic behavior for concrete. The description of the model, general parameters, and values are given in this paper. All modeling was prepared by using an FE software program. The numerical models are validated against the results of full-scale furnace, material property, push-out, and beam tests.

Thermo-hydric transfer within timber connections under fire exposure: Experimental and numerical investigations

Connections within timber structures are highly vulnerable areas when exposed to fire, especially when made of fasteners with different thermal and mechanical properties. This mechanical cohabitation can generate, because of material permeability differences, additional physico-chemical phenomena. These phenomena are affected by the coupling of heat and moisture transfers, which can alter the mechanical behaviour of timber structures. In order to improve our knowledge of the thermo-hydric timber connection, a series of experimental tests has been carried out and numerical models have been developed by taking the experimental observations into account. The experimental campaign concerns timber-to-timber and timber–steel–timber connections exposed to an “ISO 834” fire. The connections studied are real joints made of timber members, with and without a median metal plate, and maintained using bolts or dowels. The present study was conducted to examine heat transfer while taking the hydric effects at the interface between timber and steel fasteners into account. To analyse the experimental results and adjust the thermo-physical parameters for numerical modelling, numerical thermal fields, finite differences “FDM” and finite elements “FEM”, models are developed. Numerical and experimental results are in good agreement. Nevertheless, some observations are made and discussed by comparing numerical results with experimental ones.

Finite element modeling and parametric analysis of timber–steel hybrid structures

SUMMARYThis paper presents finite element modeling and a parametric analysis of prototype timber–steel hybrid structures, which are composed of steel moment‐resisting frames and infill wood‐frame shear walls. A user‐defined element was developed to model the behavior of the infill wood shear walls based on the concept of pseudo‐nail model. The element was implemented as a subroutine in a finite element software package abaqus. The model was verified by reversed cyclic test results and further used in a parametric analysis to investigate the lateral performance of timber–steel hybrid shear walls with various structural configurations. The results showed that the infill wall was quite effective within small drift ratios, and the elastic lateral stiffness of the hybrid shear wall increased when a stronger infill wall was used. In order to ensure the structural efficiency of the hybrid shear wall system, it is beneficial to use relatively strong timber–steel bolted connections to make sure the shear force can be transferred effectively between the steel frame and the infill wall. Copyright © 2013 John Wiley & Sons, Ltd.

Mechanical Properties Analysis of Steel-Timber Combined Member

Steel-timber combined member is a new kind of structural member composed of steel core and timber facing with bolt joint.This paper established the finite element analysis models of cantilever beam, and the finite element models were analyzed by the finite element package ANSYS considering the material and geometrically nonlinear.The results were compared with experimental results.Good mechanical properties were verified with comparison between data abtained from the test and calculated results.

Ductile moment-resistant steel–timber connections

This paper investigates the mechanical characterisation of a joint, suitable for different configurations within a heavy timber frame, consisting of a wooden element connected to a steel stub by means of an end-plate and glued-in steel rods. This connection system has some interesting properties in terms of mechanical performance, versatility and prefabrication. An analytical model to predict the joint response in terms of its key parameters (e.g. failure mode, ultimate resistance, stiffness and rotation capacity) is proposed and validated through an extensive experimental programme. The component method, originally proposed for semi-rigid joints in steel frameworks, is adapted in order to set up a feasible general model for steel–timber joints, enabling application of the capacity design approach and offering the required ductility for applications in seismic zones. The tests carried out indicate satisfactory agreement between theoretical and experimental results: the reliable prediction of joint failure modes allows design of moment-resistant connections that can sustain high plastic deformation without brittle rupture, with a remarkable degree of global ductility and energy dissipation under alternate loading.

Nonlinear Static Analysis of Staggered Truss Steel-Timber Combined Structure

This paper, combined the characteristics of steel structure and timber structure, conceives a new system of residential structures—staggered truss steel-timber combined structure, carries out structural arrangement and optimization design on a six-layer residence, and makes a study on its seismic performance under rare earthquake. The author uses commercial structural analysis softwareto establish a basic model, conducts pushover analysis, draws the load-displacement curve, then getsthe capacity spectrum of the model, next compares with the demand spectrum under 8 degrees (0.3g)rare earthquake, finally gets the performance point of the structure. The results show that the inter-story displacement angles can meet the limit of seismic code. Meanwhile auther analyzes the distribution and the appearance sequence of plastic hinges, plastic hinges mainly occur in the truss webs, the chords and the frame beams in succession, and the number of plastic hinges is more. Bottom columns finally appear plastic hinges. These phenomena meet the design requirement—strong column-weak beam.Finally this paper gets a conclusion that staggered truss steel-timber combined structure shows good seismic capacity.

Corrosion of ferrous- and zinc-based materials in CCA, ACQ and CuAz timber preservative aqueous solutions

Timber construction relies on connections between members. Traditionally, metallic nails and bolts are used for this. Previous research has shown that these metallic components are subject to corrosion in certain treated timbers. The American Wood Preservers’ Association AWPA E17-99 standard test has been applied using mild steel, hot-dipped galvanised steel (HDG) and 316 stainless steel coupons to examine the feasibility of using aqueous media to model corrosion rates of fastener materials in contact with timber electrolytes. In order to achieve this, comparison has been made with previously published research dealing with corrosion rates in solid timber electrolytes. The results of the corrosion testing in aqueous copper-chrome-arsenate (CCA), copper azole (CuAz) and alkaline copper quaternary (ACQ) timber preservative solutions show that aqueous electrolytes cannot be used to accurately model the corrosion behaviour of mild steel and HDG mild steel timber fixing materials. In contrast to the results obtained in treated timber, HDG steel was found to be the most active material in terms of overall metallic losses during exposure to the aqueous solutions. In addition, CCA was considerably more aggressive than either the CuAz or the ACQ preservatives. The results are discussed in terms of electrolyte pH, metallic passivation and the thermodynamic behaviour of the anodic and cathodic reactions at the mixed (corrosion) potential.

Field Press–in Test of Tapered Steel Pipe and Timber Piles

A relatively simple method was proposed in a previous study for predicting the vertical behavior of tapered piles penetrating from the ground surface. This method uses the radial cavity expansion theory to model the increase in side resistance due to the radial ground expansion as a tapered pile is being pressed, and applies the second theory of the ultimate point bearing capacity proposed by Takano N. for the point resistance. Field press–in tests were conducted on four steel sheet piles and nine timber piles at a site mainly composed of silty layers. This paper presents the test results of these four steel piles and three timber piles including one straight–sided steel pile and one straight–sided timber pile. Pile resistance obtained from field tests is compared with the predictions made by the proposed analytical method. As expected, the shaft resistance increased with the increase in taper angle and the tapered piles offered a larger resistance than the straight–sided piles. It was also found that, on sites consisting of extremely soft soil, the penetration force–displacement relationships are very sensitive to the internal frictional angle of the soil.

Axial glued-in steel timber joints?experimental and numerical analysis

This paper reports the results of an investigation on the behaviour of axially loaded joints utilising glued-in steel rods. A finite element model has been set up, in order to study the most influencing parameters for the shear stress distribution. Then, a series of tests have been carried out on joints made with Norway Spruce blocks and threaded steel bars, with different epoxy resin formulations and various ratios of hole/bar diameters. Different bar diameters have been used in experimental survey, ranging from 8 to 12 mm. Clearances of 1 or 2 millimetres have been left between bar and hole wall. The reported results are based on a sample of 240 specimens, which can be considered sufficient for statistical reliability. A statistical analysis has been performed, which confirms that: 1) the system proved to be highly efficient and reliable, with regard both to failure load and to joint stiffness; 2) with the epoxy-based adhesive used, the most important parameters affecting the strength and the stiffness of these joints seem to be the thickness of glue line and the viscosity property of the adhesive during the pouring phase; 3) these kinds of joints can be designed as ductile for specific purposes, choosing a suitable diameter of the bar.

Dependency of unit shaft resistance on in-situ stress: Observations derived from collected field data

In this study, a database comprised of 30 pullout pile load tests was collected from geotechnical literature and analyzed to investigate the dependency of unit shaft resistance on effective vertical stress. The collected database consists of steel pipe, timber, and concrete piles, with varying normalized penetration depth with respect to pile diameter, driven into loose to very dense sand. Different correlations for the uplift lateral earth pressure coefficient K, Bjerrum-Burland ratio β, and the average unit shaft resistance fave were derived using different assumptions. A comparison between measured and predicted capacities of the collected piles using the developed correlations indicated that the assumption of values of K and β that were constant with depth did not provide a reasonable fit for the measured capacities of the collected piles and thus this assumption is inappropriate. The best correlations for K and β that yield a reasonable fit to the measured capacities of the collected piles were found to be functions of sand relative density, pile diameter, and level of effective vertical stress. This indicates that average unit shaft resistance does not reach a limiting value, but rather continues to increase with depth. Moreover, the correlations for K and β in terms of effective stress revealed that average unit shaft resistance increases as pile diameter decreases and this increase depends on initial sand relative density. Comparisons of measured and predicted pullout capacities of the collected piles using the best-obtained correlations for K and β were made and compared to predictionsobtained from other methods. On the basis of these comparisons, it is concluded that the correlations for K and β in terms of effective stress give results comparable to those obtained from other methods, without stipulating limiting values for the average unit shaft resistance.

Consumption in relation to population, environment and development.

Consumption is defined as the total spending on goods investments and services that changes materials and energy and reduces availability of natural resources for the future. The rich consume on a grand scale but marginal consumption by large numbers of poor people can also deplete nonrenewable resources. This article discusses the complex relationships between consumption and population and between these two factors and environment and development. Consumption of natural resources since the mid-1900s has surpassed consumption prior to that time. The richest 20% of the global population have doubled their per capita consumption of energy meat timber steel and copper and have quadrupled the number of cars owned since 1950. The poorest 20% barely increased their per capita consumption. 40% of the total world population accounts for 6.5% of the worlds income. The US with under 5% of world population consumes about 30% of the resources. The US standard of consumption is the desired ideal in many countries but this standard is not justified. A low projected global population of 6 billion population would increase consumption by 8.4 times. Food and energy examples are used to illustrate the resource impact. Policy must move toward sustainable consumption and meet needs differently develop environmentally friendly goods and services and change the nature and extent of consumption. Policy must internalize externalities eliminate perverse subsidies calculate the ecological impact promote efficiency and sufficiency mobilize the media and set "best practices" examples. Science also has responsibilities. The future rests with decisions about how to design a better system or a default option until failures in ecological and social systems appear. Life styles should emphasize nonmaterial satisfactions. The ratio of poor to rich is 60:1 which is unacceptable. Rich citizens will eventually need to pay the price of a change in their philosophies.