SCI P118: Design of Stub Girders

The design of ‘stub girders’ is presented in a form consistent with BS 5950: Part 3. The basis of design is simplified by considering that the steel bottom chord resists tension (arising from bending action), vertical shear, and local (Vierendeel) moments across the opening. The design method is compared with the results of three full-scale stub girder tests and is shown to be conservative but reasonably accurate. Model factors for these tests were in the range of 1.0 to 1.2 when using measured material strengths, increasing to 1.2 to 1.w4 hen using design strengths.
One important observation was that the Code requirements for transverse reinforcement are unduly conservative for this form of construction. A design example is included, which covers the important aspects of the design.

SCI P129: Building Design using Cold Formed Steel Sections: Fire Protection

The fire resistance of cold formed sections is affected by the strength retention of the steel at elevated temperatures and the rate of heating of the thin steel section. Fire protection to cold formed sections may be of three forins depending on the materials used:
1. Planar protection as in floors and walls
2. Box protection
3. Profile protection.
Guidance is presented for the fire resistance of protected sections in floors or walls acting as compartment boundaries, i.e. planar protection. In this case, heat is applied from one side only and the floors or walls must satisfy the necessary insulation criterion. This guidance is based on manufacturers’ data for gypsum plasterboard and related materials.
The thickness of fire protection for conventional beams and columns is determined by using the method given in BS 5950: Part 8 for extending the existing data for hot rolled sections to cover the use of cold formed sections. Design tables are presented for typical materials and section sizes. A design summary is included at the rear of the publication which identifies the main fire protection requirements for cold formed steel sections in floors, walls and as individual beams and columns.

Properties of Self-Consolidating Concrete Containing Type F Fly Ash (thesis)

Since the introduction of self-consolidating concrete (SCC) in Japan during the late 1980’s, acceptance and usage of this concrete in the construction industry has been steadily gaining momentum. In the United States, the usage of SCC has been spearheaded by the precast concrete industry. Good SCC must possess the following key fresh properties: filling ability, passing ability, and resistance to segregation. In order to reduce segregation, SCC mixes are typically designed with high powder contents, and contain chemical admixtures such as superplasticizers and viscosity modifying admixtures (VMA). This tends to increase the material cost of SCC, however one way to reduce the material cost is through adequate mix proportioning and the addition of supplementary cementitious materials such as fly ash. Millions of tons of fly ash are generated annually in Illinois; however Class F fly ash is more often landfilled than used. Incorporation of Class F fly ash in self-consolidating concrete as a means to replace portions of cement can decrease the cost of SCC, as well as further the sustainable development of concrete. An experimental program, aimed at investigating the behavior of SCC containing Class F fly ash has been carried out. The fresh state properties of the concrete were assessed using methods of segregation and flow. The rheology of the paste matrix was also characterized and compared with a previously developed paste rheology model. Finally, some hardened state properties of the concrete were evaluated. The objective of this research is to improve the understanding of the properties of SCC containing Class F fly ash and to provide information that could be used towards the commercialization of such a concrete. The results indicate that it is possible to develop a SCC containing Class F fly ash that is high performing in its fresh state. Furthermore, the addition of fly ash was shown to reduce superplasticizer dosage, increase workability, and increase overall chloride permeability resistance. In addition, it was determined that the difference of densities between the aggregate and matrix influence the results of a previously developed paste rheology model.

Frost and Scaling Resistance of High-Strength Concrete

The primary purpose of this work was to assess the effect of air entrainment and time of surface finishing operations on the frost durability and scaling resistance of high-strength concrete. The conditions under which entrained air is necessary to produce a frost-resistant mixture are explored, particularly in light of current ACI 318 provisions for air content. The laboratory program consisted of the production of six concrete mixtures with water/cement ratios of 0.50, 0.45, 0.40, 0.35, 0.30, and 0.25; each at three levels of air content: non-air entrained, 4%, and 6%. No supplementary cementing materials were used. Frost resistance was investigated as a bulk or interior concrete property, via modified ASTM C 666, and as a surface property, via ASTM C 672. Both tests were initiated at 28 days with the same curing conditions applied to the specimens. The influence of time of surface finishing on the scaling resistance was investigated by finishing the scaling specimens at two different times relative to the time of initial set as defined by ASTM C 403. Additionally for each mixture, compressive strength (ASTM C 39), rapid chloride permeability (ASTM C 1202), and microscopic analysis of the air void system (ASTM C 457) were performed. For the mixtures investigated here, it was possible to obtain frost resistance based on the modified ASTM C 666 without air entrainment for w/c = 0.35 or less, while entrained air was necessary for mixtures with w/c greater than 0.40. As far as scaling resistance is concerned, no air entrainment was necessary for mixtures with w/c of 0.25, while entrained air was necessary for mixtures with w/c greater than 0.25. It was observed that the ACI 318 provisions for frost durability are somewhat conservative. While ACI 318 requires air entrainment for all mixtures subject to freezing and thawing, mixtures studied here with w/c of 0.25 and no intentionally entrained air were shown to be frost resistant. Further, properly air-entrained mixtures with w/c of 0.50 were frost resistant, even though the w/c was in excess of the 0.45 required by the ACI 318 provisions
for freeze-thaw durability.

Thickness Design Systems for Pavements Containing Soil-Cement Bases

With the proposed move to a national Mechanistic Empirical Pavement Design Guide (MEPDG) the Portland Cement Association (PCA) initiated this study to review the proposed models for Soil-Cement (S-C) base and Cement Modified Soils (CMS). To provide a smooth transition to the new design procedures researchers evaluated the laboratory procedures needed to provide the input material properties for resilient modulus (MR) and modulus of rupture (Mr). In addition, software tools were developed to introduce the concepts of mechanistic design to pavement designers.
Researchers found that the traditional laboratory resilient modulus test is extremely difficult to run on S-C samples. The induced strains are very low, and the sample preparation and finishing have a major impact on repeatability. A new test including measurement of the seismic velocity appears to provide much more potential. A good correlation was obtained between both tests. The use of unconfined compressive strength to estimate both resilient modulus and modulus of rupture also appears reasonable. Recommendations are provided in this report. A summary was also made of tools for measuring resilient modulus in the field. The use of the Falling Weight Deflectometer (FWD), Portable Seismic Pavement Analyzer, and lightweight FWD are described. From FWD data, the resilient modulus values obtained in the field are substantially less than those measured in the laboratory.
To evaluate the proposed MEPDG model for S-C bases, an attempt was made to calibrate the model with accelerated pavement test data collected by the PCA in the 1970’s. Calibration factors were developed for the proposed model. In addition, a model based on the PCA recommendations was also calibrated. Both calibrated models were built into two software packages developed in this study. These packages are intended as training tools for introducing the concept of handling the S-C or CMS layer in mechanistic-empirical design systems.