Behavior of C- and Z-purlins under wind uplift

INTRODUCTION Cold-formed steel lipped channel (C-) and Z-purlins are used widely in the roofs of metal buildings. They are easy and economical to fabricate and erect. However these sections are weak in the lateral direction and in torsion. In order to use their full bending capacity in the strong direction, they must be braced in the lateral direction and against twisting. Roof panels which are connected to the purlins do provide to some extent such bracing effect by virtue of their shear rigidity and resistance to local bending at the connections. Wind uplift is an important design condition for roof purlins. The objective of the research reported herein was to develop simple design equations for C- and Z-purlins subjected to uplift. The previous work reported in Refs. 2 through 4 based on the classical theory of torsional-flexure resulted in computer programs for the analysis of the problem. The classical theory of torsional-flexure due to its complexity was not suitable for treating the effects of local buckling and post-buckling behavior on the overall behavior. Furthermore, this approach was not extended to include the effects of initial sweep and twist of purlins. The importance of these parameters was observed in several large scale tests. The theory was shown to be satisfactory for predicting deflections but not the ultimate loads. The discrepancies were larger for thinner sections indicating the importance of local behavior of the component plate elements of the sections. In the first phase of the present research reported in Ref. 1, work was initiated to include the above parameters in a design formulation. The basic approach used in Ref. 1 was that given in Section 3 of Part III of Ref. 5. This approach also has several deficiencies. First, a sudden bifurcation type is the basic behavior mode assumed in that approach. Namely, it is assumed that the compression flange of a purlin does not deflect laterally until failure. The actual behavior is clearly not so. The compression flange deflects laterally from the start of loading. Second, the effect of initial sweep and twist is not accounted for. These and several other additional deficiencies of that approach have been eliminated by the new approach derived in the present research. This new approach will be discussed in detail in Chapter 2. Failure criteria will also be discussed in this chapter. Simplications to the general solutions obtained in Chapter 2 will be presented in Chapter 3. Large scale and component tests by the authors and by a steel manufacturer will be described in Chapter 4. The experimental and analytical results will be compared in Chapter 5. Finally, a summary of the work and the conclusions will be presented in Chapter 6

ENHANCEMENT OF CONCRETE PIPES THROUGH REINFORCEMENT WITH DISCRETE FIBERS

An industrial-scale production and experimental investigation was conducted in order to evaluate the constructability and structural performance of different concrete pipes incorporating discrete synthetic fibers. The results indicated that synthetic fibers enable design of plain concrete pipes with a desired balance of strength and ductility. Analytical models were developed for predicting the load-carrying capacity of concrete pipes without steel reinforcement that are reinforced with discrete fibers

A General Rule for the Influence of Physical Damping on the Numerical Stability of Time Integration Analysis

The influence of physical damping on the numerical stability of time integration analysis is an open question since decades ago. In this paper, it is shown that, under specific very general conditions, physical damping can be disregarded when studying the numerical stability. It is also shown that, provided the specific conditions are met, analysis of structural systems involved in extremely high linear-viscous damping is unconditionally stable. A secondary achievement is that, when the linear-viscous damping increases, the numerical damping may increase or decrease

Aerated Concrete Produced Using Locally Available Raw Materials

Aerated concrete materials were developed with abundant natural materials. Aerated concrete can provide insulating qualities complemented with secondary structural attributes when used as core in sandwich composites for building construction. A hybrid binder that comprised lime and gypsum was used. Different foaming agents were considered for production of aerated concrete, including saponin that is found abundantly in different plants. Different formulations were considered, and the stability of the foam structure as well as the density and early-age compressive strength of the resulting aerated concrete were evaluated. One formulation comprising lime-gypsum binder with saponin foaming agent, with a density of 0.53 g/cm3, was further characterized through performance of thermal conductivity, split tension, flexure, elastic and shear modulus and sorptivity tests. The results pointed at the satisfactory balance of qualities provided by the aerated concrete when compared with alternative aerated concrete materials

A SUSTAINABLE APPROACH TO IMPROVEMENT OF CORROSION PROTECTION COATINGS FOR STEEL STRUCTURES

            Corrosion is a primary factor compromising the safety and service life of steel structures. Corrosion protection coatings are generally employed for protection of the steel structures that are exposed to different aggressive environments. This research evaluated the use of biobased ion exchangers as a sustainable means of improving corrosion protection coatings. Two base polymer coatings (vinyl and coal-tar epoxy) were considered.  The following types and dosages of biobased ion exchangers were evaluated in these coatings: (i) strong-base ion exchange cellulose in OH, PO4, SiO3, BO3, NO2, SO4 and NO3 forms at 1% by weight of resin; (ii) weak-acid starch citrate ion exchanger in H form at 1 wt.%; and (iii) strong-base ion exchange cellulose in OH form at 2 wt.%. In addition, a strong-base ion exchange resin in OH form was considered at 1 and 2 wt.% as control.  Different coating formulations were evaluated based on the outcomes of salt-fog corrosion, moisture resistance, pull-off strength, and abrasion resistance tests. The introduction of certain biobased ion exchangers in protective coatings was found to be an effective means of achieving improved levels of corrosion resistance, adhesion capacity, moisture stability and abrasion resistance

Alkali-Activation of Non-Wood Biomass Ash: Effects of Ash Characteristics on Concrete Performance

Combustion of biomass is increasingly practiced for power generation. Unlike coal ash, the combustion ashes of biomass do not offer significant value in Portland cement concrete production. An experimental study was conducted in order to assess the value of the combustion ashes of different non-wood biomass types towards production of alkali activated binders for concrete production. The results indicated that concrete materials with a desired balance of fresh mix workability, set time and compressive strength can be produced used alkali activated non-wood biomass ash binders. Correlations were drawn between the concrete engineering properties and different non-wood biomass ash characteristics. It was found that statistically significant relationships exist between the concrete properties and the non-wood biomass ash degree of crystallinity and solubility. These two ash characteristics were also found to be correlated. It was concluded that the suitability of non-wood biomass ash for use in production of alkali activated concrete can be assessed based on its degree of crystallinity

Efficient Static Analysis of Assemblies of Beam-Columns Subjected to Continuous Loadings Available as Digitized Records

Beams, beam-columns, columns, and frames, are of major importance in structural engineering, and especially buildings and infrastructures analysis and design. In some cases, these structural members are subjected to static loadings, that though are continuous with respect to the longitudinal axes, are available as digitized records. Finite element analysis of assemblies of these members may be computationally expensive when the loading is digitized densely. In order to reduce this computational effort, attention is paid to a technique originally proposed in 2008 for reduction of the computational effort in time integration analysis. In view of the convergence-based nature of this technique, in this paper, the technique is adapted to static analysis of assemblies of beam-columns subjected to digitized loadings. The good performance of the adapted technique is demonstrated from different points of view, and is compared with the performance of the technique in time integration analysis

Impact resistance of deflection-hardening fiber reinforced concretes with different mixture parameters

YesThe impact behavior of deflection-hardening High Performance Fiber Reinforced Cementitious Concretes (HPFRCs) was evaluated herein. During the preparation of HPFRCs, fiber type and amount, fly ash to Portland cement ratio and aggregate to binder ratio were taken into consideration. HPFRC beams were tested for impact resistance using free-fall drop-weight test. Acceleration, displacement and impact load vs. time graphs were constructed and their relationship to the proposed mixture parameters were evaluated. The paper also aims to present and verify a nonlinear finite element analysis, employing the incremental nonlinear dynamic analysis, concrete damage plasticity model and contact surface between the dropped hammer and test specimen available in ABAQUS. The proposed modelling provides extensive and accurate data on structural behavior, including acceleration, displacement profiles and residual displacement results. Experimental results which are further confirmed by numerical studies show that impact resistance of HPFRC mixtures can be significantly improved by a proper mixture proportioning. In the presence of high amounts of coarse aggregates, fly ash and increased volume of hybrid fibers, impact resistance of fiberless reference specimens can be modified in a way to exhibit relatively smaller displacement results after impact loading without risking the basic mechanical properties and deflection-hardening response with multiple cracking

Properties of hemp fibre reinforced concrete composites

This research is concerned with the mechanical and physical properties of hemp fibre reinforced concrete (HFRC). An experimental program was developed based on the statistical method of fractional factors design. The variables for the experimental study were: (1) mixing method; (2) fibre content by weight; (3) aggregate size; and (4) fibre length. Their effects on the compressive and flexural performance of HFRC composites were investigated. The specific gravity and water absorption ratio of HFRC were also studied. The results indicate that the compressive and flexural properties can be modelled using a simple empirical linear expression based on statistical analysis and regression, and that hemp fibre content (by weight) is the critical factor affecting the compressive and flexural properties of HFRC