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

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

Plastic shrinkage cracking and bleeding of concrete prepared with alkali activated cement

Restrained shrinkage cracking that appears on concrete surfaces during construction, or while concrete in the curing process adversely affect the long-term durability and other performance attributes of concrete-based-infrastructures. This study investigates the effects of early-age surface cracking on restrained shrinkage concrete made of alkali activated cement. Concrete produced using this class of cement differs from ordinary Portland cement concrete in terms of surface qualities and some other properties. Bleeding which could be a main cause of plastic shrinkage cracking was measured and compared with that of Portland cement. Rheological tests were performed to gain further insight into factors that may influence the early-age performance of the cement paste. Portland cement was used as control for comparative assessment of the alkali activated cement performance. Experimental test showed that alkali activated cement improved the characteristics of the newly produced concrete. The concrete prepared using alkali activated cement has low tendency to bleeding and higher resistance to plastic shrinkage, also, the viscosity and yield stress of the alkali activated cement paste were relatively higher when compared to those of ordinary Portland cement paste. Test data collected from rheological and bleeding tests on the alkali activated cement concrete were used to explain its desired resistance to plastic shrinkage cracking

Mechanical Properties of Hybrid Fiber Reinforced Lightweight Aggregate Concrete Made with Natural Pumice

The purpose of this study is to improve the ductility of pumice lightweight aggregate concrete by incorporating hybrid steel and polypropylene fibers. The changes in mechanical properties and also bulk density and workability of pumice lightweight aggregate concrete due to the addition of hybrid steel and polypropylene fibers have been studied. The properties were investigated include bulk density and workability of fresh concrete as well as compressive strength, flexural tensile strength, splitting tensile strength and toughness of hardened concrete. Nine concrete mixtures with different volume fractions of steel and polypropylene fibers were tested. A large increase in compressive and flexural ductility and energy absorption capacity due to the addition of steel fibers was observed. Polypropylene fibers, on the other hand, caused a minor change in mechanical properties of hardened concrete especially in the mixtures made with both steel and polypropylene fibers. These observations provide insight into the benefits of different fiber reinforcement systems to the mechanical performance of pumice lightweight aggregate concrete which is considered to be brittle. These results provide guidance for design of concrete materials with reduced density and enhanced ductility for different applications, including construction of high-rise, earthquake-resistant buildings

Optimization of ultra-high-performance concrete with nano- and micro-scale reinforcement

Ultra-high-performance concrete (UHPC) incorporates a relatively large volume fraction of very dense cementitious binder with microscale fibers. The dense binder in UHPC can effectively interact with nano- and microscale reinforcement, which offers the promise to overcome the brittleness of UHPC. Nanoscale reinforcement can act synergistically with microscale fibers by providing reinforcing action of a finer scale, and also by improving the bond and pullout behavior of microscale fibers. Carbon nanofiber (CNF) and polyvinyl alcohol (PVA) fiber were used as nano- and microscale reinforcement, respectively, in UHPC. An optimization experimental program was conducted in order to identify the optimum dosages of CNF and PVA fiber for realizing balanced gains in flexural strength, energy absorption capacity, ductility, impact resistance, abrasion resistance, and compressive strength of UHPC without compromising the fresh mix workability. Experimental results indicated that significant and balanced gains in the UHPC performance characteristics could be realized when a relatively low volume fraction of CNF (0.047 vol.% of concrete) is used in combination with a moderate volume fraction of PVA fibers (0.37 vol.% of concrete)

Optimization of ultra-high performance concrete, quantification of characteristic features

An optimization experimental program was designed to identify a desired balance of key mix design parameters for an economical ultra-high-performance concrete (UHPC) mixture. The following mix design parameters were evaluated: superplasticizer content, coarse-to-fine aggregate ratio and steel fiber volume fraction. The values of packing density, water film thickness and excess paste film thickness were calculated considered in the optimization experimental program. The trends in the effects of packing density, water film thickness and excess paste film thickness on compressive strength and fresh mix flow were investigated. The results were used to identify viable ranges of these defining characteristics for the category of UHPC. Response surface analysis of the fresh mix flow and the hardened concrete compressive strength test results led to identification of the optimum values of mix design parameters. The optimum mix was found to produce a desired balance of fresh mix flow and hardened concrete compressive strength