Most maintenance problems associated with industrial concrete floors result from the joints. This paper emphasizes a method to eliminate saw-cut joints in slabs-on-grade by the use of steel fiber reinforced concrete (SFRC) only. The performance of the composite material is directly linked with the choice of a specific concrete mix design and an improved technique to uniformly mix a high dosage of steel fibers. Tests and experience have shown that high level post-cracking ductility of the SFRC can control micro-cracking caused by flexural and shear stresses combined with restrained shrinkage. The proposed design approach, based on the yield-line theory, gives an objective view of the safety factor in relation to the ultimate state. Case studies demonstrate that typical areas of 25,000 ft² (2322 m²), without saw-cut joints, are regularly achieved by experienced contractors with relevant site quality control. Practical site aspects such as armored contraction joints, slab details, aspect ratio, installation techniques etc., are an integral part of the case study as well. The second part of this paper details the use of this technique for structural applications such as suspended slabs on piles and mat foundations. To demonstrate the structural capacity of concrete solely reinforced with a high dosage of steel fibers, real scale tests and practical case studies are presented.

Both short and long-term performances of repaired or strengthenedconcrete structures using external FRP bonding are greatly affected by states ofbonding substrates, which are covercrete and may have experienced various damages.One of them is frost damage in cold regions. This paper intends to investigate how theinitial frost damages in concrete influence the static and fatigue bond performances ofCFRP/concrete interfaces. Concrete specimens were exposed to freeze and thaw cyclesbefore being bonded with CFRP sheets. The initial frost damage of concrete wascontrolled approximately at three different levels in terms of its relative dynamicmodulus of elasticity, which was 100% (non frost damage), 85% and 70%, respectively.Test results showed that failure modes of CFRP/concrete bonded joints with initial frostdamage in concrete were the delamination of covercrete. By contrast the joints withoutinitial frost damage failed in a thin concrete layer as usual. Moreover, CFRP/concretejoints with and without initial frost damage showed different manners in their interfacebonding strength and stiffness. If the initial frost damage existed in concrete substratethe effective bond length of CFRP/concrete joints was increased due to the decrease ofthe bonding stiffness and interfacial fracture energy. Fatigue testing results indicatedthat the linear slopes of S-N curves of CFRP/concrete bonded joints were not influencedby the initial frost damage. The initial frost damage did not shorten the fatigue life ofCFRP/concrete joints if a same relative tensile stress level was kept in the FRP sheets,where the relative tensile stress level was defined as a ratio of the applied tensile forcein FRP sheets for the fatigue tests to the maximum static pullout one achieved in eachtest series.

The behavior of beam-column connections in WC frame structures has been extensively studied since the 1960’s. These studies have served as the basis for design guidelines for WC joints, in which detailing requirements and stress limits are given to control damage and deterioration of strength and stiffness in the connections. However, no particular attention is paid to the deformation in the joint region and its relation to the connection strength. In this paper a model is presented to evaluate the shear strength of WC joints for various levels of joint shear distortion. The joint model is based on the state of plane strains in the connection through the development of a ratio between the joint principal strains, which was determined from experimental results. Based on the joint model, stress limits are proposed for interior and exterior joints for a shear distortion of 1%. These limits are similar to those recommended by ACI-ASCE Committee 352 for exterior connections. However, they are lower than those recommended for interior joints. The detrimental effect of eccentricity on joint strength is also estimated. Further analyses are required to fully quantify the effect of joint type and details on the principal strain ratio, and thus on joint strength.

A new design capability for automated formulation of optimal truss models (strut-and-tie models) is presented and illustrated with example designs of a variety of disturbed regions of reinforced and pre-stressed concrete structures, including deep beams with holes, continuous beams, and comer joints. The design method selects the optimal geometry of the strut-and-tie layout, determining the proper positioning of tensile ties and compressive struts to minimize the amount of reinforcing steel needed in the tension ties of the truss model for the region being designed. Two practical parameters are under control of the design engineer running the computer program-a reinforcement layout practicality factor which can be used to force the reinforcement layout into strictly horizontal and vertical bars (which will require additional reinforcement volume beyond the true optimal value), and a stress redistribution factor which can be used to control the amount of redistribution needed in developing the full capacity of the truss model after cracking has occurred.

Equivalent macromodel-based analytical tools, comprised of flexibility-based element models, are used to accurately represent the non-linear moment-curvature (force-deformation) response characteristics in structural systems using columns of reinforced concrete (RC) or composite steel sections encased in reinforced concrete (SRC), structural steel beams, and composite beam-column joints. To facilitate the modeling of inelastic deformations in joint regions, a panel element capable of representing joint shear distortions and joint bearing deformations was developed and incorporated into an existing computer program, IDARC. The inelastic shear-deformation characteristics of the joint panel were partly established from guidelines published by an ASCE Task Committee (1). Various hysteretic control parameters for members of the subassemblage, such as strength degradation, stiffness deterioration, and pinching (slip), were quantified based on observed experimental response. Potential failure modes in the steel beam, RC or SRC column, and composite joint of the frame subassemblage can be represented in the proposed formulation. Experimental subassemblage testing performed at Cornell University (2) was used to validate the analytical platform. It is shown that the revised IDARC program can be used for seismic evaluation of composite structures and for development of design guidelines to ensure desirable mechanisms in RCBRC structures.