International Concrete Abstracts Portal

This paper reports design recommendations for flexural cracking and short-term deflection control in reinforced concrete (RC) beam-type elements. The proposed crack control procedures, which have evolved from existing design provisions in ACI 318-08 and AASHTO LRFD 2007, aim at controlling flexural cracking either directly -through the calculation of crack widths-, or indirectly -by prescribing a maximum spacing for the tension reinforcing bars-. The main feature of the proposed crack control procedures is that they are explicitly set up as a function of a limiting crack width value. This approach gives designers the ability to control specific serviceability requirements stipulated by the Owner/User of the structure and is very convenient in those instances where the limiting crack width is less than that tacitly linked to the ACI 318-08 crack control procedure. The proposed deflection control procedures are indirect in nature, aiming at controlling deflections by specifying maximum span/depth ratios based on the concept of limiting curvature and also as a function of both the deflection/span ratio and the maximum allowable crack width. Even though the serviceability design formulations are general in form, emphasis is given to RC beam-type elements in marine infrastructure.

This paper describes the evaluation of the in-service performance of a short-span bridge deck built with FRP reinforced concrete (RC) panels. The Walters Street Bridge consists of nine FRP-RC panels connected with shear keys. The multi-panel bridge deck was monitored for a period of four years by load testing the bridge deck with standard trucks and collecting deflection data. Experimentally derived factors such as stiffness degradation, and load fraction distribution between panels were computed from field deflections and compared with AASHTO provisions and results of an analytical study. The load fraction values, which assess the transverse load distribution, were consistent along the 4-year period. Load tests involving the use of two trucks at the same time were performed in the last year with the purpose of finding the most critical deflection under service load conditions, which was compared to allowable AASHTO live load deflections. Analytical deflections were calculated using ACI guidelines and structural analysis methods. The load tests, as well as the analytical results, revealed that the deflections were well within the recommended AASHTO values.

Composite materials and high strength adhesives are becoming popular for various structural repair jobs. These materials provide good solutions for repairing, and retrofitting concrete structures. In this system repair work can be done within a short time, without using much labor, and the repair materials generally do not alter the geometric shapes of the original structural member. However, the interactive behavior (both short and long term) of un-bonded post-tensioned structural components, when repaired and retrofitted with composite materials is not yet properly understood. The current research was conducted to understand this. Eleven 12’-0" long beams B1 thru B11, were loaded close to their ultimate values. The tests were stopped based on three criteria: excessive cracking, or pre-stressing load reaching over 80%-85% fpu, or deflection reaching twice the allowable deflection. The cracked beams were repaired with varying amount of composite materials adhesives, and tested again. The beams were named B1CR, B2CR, B3EgR and so on, where CR represents repair with carbon FRP and EgR represents repair with e-glass FRP. The tests were stopped again based on the above three criteria. Using Carbon and E-glass FRP and adhesives, a very effective repairing and retrofitting system has been developed. The load carrying capacities and deflections of these beams and that of the original un-cracked beams were compared. Various repairing schemes were adopted. Attempts were made to find the minimum usage of the composite materials, prevent diagonal shear cracking, and prevent sudden compression failures. The changes in post-tensioning forces, the effect of having mild steel in the tension zone, and crack propagation at ultimate stage were recorded and discussed here.

This paper presents an overview of the requirements for deflection of beams and slabs in the draft Brazilian Code for concrete structures, NBR 6116:2000. Firstly, the Brazilian Code recommendations for deflection computations and allowable limits are described, and then these provisions are compared with those of section 9.5 of ACI 316-99. The paper also includes a numerical example to illustrate how the new proposals are applied to structural design. It is observed that the general criteria of the two codes are similar, but some differences are pointed out regarding minimum thickness requirements, load conditions, effective moment of inertia for continuous beams and the values of modular ratio, modulus of rupture and allowable deflections.

Based on four strength parameters testing of three high-performance concrete (HPC) design mixes and parametric studies, the following conclusions have been made. Creep and shrinkage strains of HPC are lower than those in conventional concrete. Amount and type of coarse aggregates affect the value of modulus of elasticity. The modulus of elasticity of HPC should be determined through experiments with local materials. Beam sections that have large bottom flange are efficient for HPC application. The most significant property of HPC prestressed beam is compressive strength at release. Allowable compression at release has the most impact on span capacity, while allowable tension at service has minor impact. Prestress loss can be reasonably predicted by either the proposed method or AASHTO LRFD Lump Sum method. PCI deflection multipliers at final time are not accurate. The proposed multipliers which are the functions of creep coefficient can be used for conventional and HPC members.