International Concrete Abstracts Portal

This paper presents a novel framework of analysis to assess the resistance of existing reinforced concrete (RC) members experiencing spatial variability of crack patterns and spatial variability of concrete mechanical properties. The spatial variabilities are considered by using digital image processing (DIP) to map crack patterns onto three-dimensional (3-D) nonlinear finite element (NFE) models, where the concrete mechanical properties (compressive strength, tensile strength, damage, and modulus of elasticity) are spatially varied using random fields (RFs) to form random NFE (RNFE) models. The framework was developed and applied to assess a corroded RC beam (to determine the distribution of the resistance) and column (to determine the reliability of the column at the ultimate limit state [ULS]). Research findings indicate improved accuracy in assessing the resistance of the corroded members up to 20%, and the adaptivity of the developed framework for performing reliability analysis of existing RC structures.

This paper presents the effectiveness of various reinforcing schemes in the end zones of prestressed concrete bulb-tee girders. The default girder, provided by a local transportation agency, includes C-bars and spirals intended to control cracking, and is analyzed using three-dimensional finite element analysis. The formulated models are used to evaluate the breadth of end zones, strain responses, cracking patterns, damage amounts, and splitting forces, depending upon the configuration of the end-zone reinforcement. The number of C-bars is not influential in developing strand stress along the girder. The maximum principal stresses exceed the conventional limit within h/4 of the girder end, where h is the girder depth; however, the 3h/4 limit adequately encompasses the stress profiles, particularly in the web of the girder. The maximum tensile strain in the concrete varies with the elevation of the girder, and the inclined strands cause local compression in the C-bars, while spiral strains are independent of the number of bars. By positioning the C-bars, the vertical strain of the concrete decreases by more than 15.9%, which can minimize crack formation. Whereas the short-term crack width of the girder may not be an immediate concern, its long-term width is found to surpass the established limit of 0.18 mm (0.007 in.). In this regard, multiple C-bars should be placed to address concerns about undesirable cracking. The splitting cracks in the girder, resulting from the strand angles and eccentricities, can be properly predicted by published specifications within the range of 0.2h to 0.7h, beyond which remarkable discrepancies are observed in comparison with a refined approach. From a practical perspective, two to three No. 6 or No. 7 C-bars spaced 150 mm (6 in.) apart are recommended in the end zones alongside welded wire fabric.

This study used finite element analysis to examine how tendon configuration affects the temperature behavior of post-tensioned concrete structures during fire exposure. The thermal behavior of various tendon configurations was modeled, showing good agreement with experimental data. Parametric studies found that unbonded single-strand tendons (S) and prestressing (pretensioned) strands (R) had lower thermal resistance than bonded post-tensioned tendons (B), unbonded post-tensioned tendons (U), and grouted extruded-strand tendons (G). The S and R specimens stayed at or below the critical temperature for one-way slabs, validating current safety codes. The B, U, and G specimens remained well below critical temperatures, indicating that a thinner concrete cover might suffice. These findings highlight the need to consider tendon configuration in structural fire-resistance evaluation and incorporate heat resistance assessment to ensure the safety and efficiency of prestressed concrete structures during fires.

Slabs-on-ground supporting storage racks are often subjected to concentrated uplift under building code seismic forces. While methods for determining slab-on-ground capacity for downward loads are well defined, guidance for resistance to uplift has been limited and relies on finite element analysis. A simplified approach is presented for calculating slab-on-ground uplift capacity as a function of slab thickness, reinforcing content, and storage rack frame depth. Testing is conducted on small-scale concrete samples in bending to obtain the material properties. Model slabs are created and tested for an upward and downward force couple representing concentrated seismic uplift on a reinforced slab-on-ground. The plastic hinge failure mechanism of the slab samples is correlated with finite element models, and straightforward formulas are developed to produce a table of uplift capacities for common storage rack and slab-on-ground configurations.

Reinforced concrete walls are commonly used in low- and mid-rise construction because they provide high strength, stiffness, and durability. In regions of low and moderate seismicity, ACI 318 Code requirements for minimum reinforcement ratio and maximum reinforcement spacing typically control over strength-based requirements. However, these requirements are not well-supported by research. The current study investigates requirements for the amount and spacing of reinforcement using experimentally validated nonlinear finite element modeling. For lightly reinforced concrete walls subjected to out-of-plane loading: 1) peak strength is controlled by concrete cracking; and 2) residual strength depends on the number of curtains of steel. Walls with very low steel-fiber dosages were also studied. Results show that fiber, rather than discrete bars, provides the most benefit to wall strength, with fiber-reinforced concrete walls achieving peak strengths more than twice that of identically reinforced concrete walls.