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An experimental investigation was conducted on the shear behavior of deep beams made with steel fiber reinforced high performance concrete (HPC). Twenty-six beam specimens with various shear span-effective depth ratios, steel fiber contents, amounts of vertical and horizontal web reinforcements were tested under static loads. In addition to the strength test, extensive instrumentations were designed for the measurements of average strains of reinforced concrete in the shear span and strains of web reinforcements. The web-shear cracking initiated as the first inclined shear crack. About 30% increase in the inclined shear strength and 25% increase in the ultimate shear strength can be achieved with addition of 1 .O% steel fiber for specimens having a/d= 1 .5. The strain of vertical web reinforcements became negative and the horizontal web reinforcements were stretched to yield state for specimens having a/d ratios approach 0.5. The measured load-deformation relationships of reinforced concrete and strains of web reinforcements were compared with the prediction of the softened truss model of steel fiber reinforced concrete proposed by other investigators. Good correlation was found from the comparisons.

The current design recommendations for concrete deep beams given in the ACI Code, Canadian Code, CEB-FIP Model Code, CIRIA Guide-2, etc., are based on research results on normal strength concrete. As such, these design recommendations may not be directly applicable to deep beams made of high-strength concrete. A summary of the authors' recent research on the shear behavior of deep beams made of high-strength concrete is presented. Experimental results on the ultimate shear strengths of single-span, continuous, and slender deep beams as affected by the strength of concrete, shear-span-to-depth ratio, and slenderness ratio, are compared to various design methods. It is found that the ACI method is overly conservative for all cases, the Canadian Code method is unconservative for higher strength concrete, the CEB-FIP method gives somewhat scattered predictions, and the CIRIA Guide-2 is slightly unconservative for all cases. A minor modification on the CIRIA Guide-2 method is shown to yield a reliable method for all the cases investigated.

In general, the structural member using high-strength concrete is accompanied by high brittleness, which may result in the unexpected dangerous failure. For economy and safety, high-strength concrete may be used for compressive members (vertical members) and low-strength concrete for flexural members (horizontal members). ACI 318-89 recommends that when the specified compressive strength of concrete in the column is greater than 1.4 times that specified for the floor system, the column concrete shall extend 600 mm into the slab from column face to avoid unexpected failure. The structural behavior of beam-column joints with two different compressive strengths of concrete for the beams and the columns has not been investigated adequately. ACI-ASCE Committee 352 recommends that for joints that are part of the primary system for resisting seismic lateral loads, the sum of nominal moment strengths of the column sections above and below the joint ( M c), calculated using the axial load, which gives the minimum column moment strength, should not be less than 1.4 times the sum of the nominal strengths of the beam sections at the joint ( M b). Thus, those recommended values should be examined before high-strength concrete can be used with confidence and convenience in structural members. The results showed that the ACI 318-89 extension distance of 600 mm is safe at least for members up to 300 mm in total depth, and the 2h (h is overall depth of the beam) extension distance was found to be safe also for members under flexural loading with a column-to-beam flexural strength ratio of 1.8.

Recently, there has been a great demand for high-quality concrete and concrete structures with high performance. In this context, silica fume is one of the most remarkable mineral admixtures that can give concrete high performance, such as high workability, strength, and durability. However, it is unclear as to the types of form silica fume takes in concrete, mortar, and cement paste. Some researchers point out that silica fume may be in high agglomeration. Therefore, it is very important to disperse silica fume in concrete effectively to get high-performance concrete. Consequently, this paper deals with the effect of physical treatment (ultrasonic homogenizer) and chemical treatment (superplasticizer) of silica fume on the properties of mortar. In this study, different silica fumes were used, one Japanese and five imported. The investigated properties of mortar were workability (flow values), compressive strength, and total pore volume. The study resulted in the following conclusions: 1) Silica fumes in the Japanese market were highly agglomerated in the natural state. This agglomeration of silica fume can be broken up by using some treatment methods, such as ultrasonic homogenizer and superplasticizer. 2) Physical treatment (ultrasonic homogenizer) before mixing mortar was useful to improve compressive strength and to decrease total pore volume of mortar containing silica fume. The use of superplasticizer could result in highly workable mortar. 3) The effectiveness of ultrasonic homogenizer treatment and that of superplasticizer treatment are different.

The latest developments in concrete platform concepts for deep water and floating structures have indicated the need for further development in the field of practical concrete technology. Paper presents some of the most significant factors in this challenge such as increased compressive strength, improved workability, and stability of fresh concrete, use of high-strength lightweight aggregate concrete, measures to improve the concrete E-modulus, and utilization of variable concrete density to optimize the platform design. This has been achieved through further development of the constituent materials, refinements of the mix design, and advancements in production methods, as well as the use of high-quality lightweight aggregates.