Magazine Title: ACI Structural Journal

 

Title of article: Seismic Behavior of 150 MPa (22 ksi) Concrete Flexural Elements

Author: Abdelsamie Elmenshawi and Tom Brown

 

Issue: May 2010

 

An experimental program was carried out to investigate the seismic behavior of flexural elements constructed with concrete strengths up to 150 MPa (22 ksi), at which strength the literature is very scarce. Ten carefully chosen beam-column sub assemblages were tested such that the column stub had no axial compressive force and was connected to the laboratory strong floor. The beam end connected to the actuator to displace horizontally according to a predefined displacement scheme. Each specimen consisted of a 250 x 350 x 1000 mm (10 x 14 x 39 in.) beam cast monolithically with a 300 x 450 x 1050 mm (12 x 18 x 41 in.) column stub. The test variables included the concrete compressive strength (30, 70, and 150 MPa [4, 10, and 22 ksi]), the bottom/top reinforcement ratio (0.33 and 1.0), the transverse reinforcement ratio (0.8 and 1.6%), and the shear span-depth ratio (2.0 and 3.0). The research aimed at examining the cracking behavior, hysteretic behavior, energy dissipation, ductility, flexural strength, and flexural rigidity of the tested specimens.

 

Magazine Title: ACI Structural Journal

 

Title of article:  Flexural Cracks in Fiber-Reinforced Concrete Beams with Fiber-Reinforced Polymer Reinforcing Bars

Author: Won K. Lee, Daniel C. Jansen, Kenneth B. Berlin, and Ian E. Cohe

 

Issue: May 2010

 

Fiber-reinforced polymer (FRP) reinforcing bars have attracted considerable attention for applications where corrosion of steel reinforcement is problematic. Due to the generally low elastic modulus and poor bond characteristics of FRP as compared to steel reinforcing bars, the use of FRP results in larger crack widths under service loads. Fiber-reinforced concrete (FRC) is proposed for use with FRP to reduce crack widths. The work presented herein includes the results from 16 beams tested under four-point bending with either Grade 420 (Grade 60) steel or FRP reinforcing bars, and either plain concrete or FRC. A modified Gergely-Lutz model was applied to the measured crack widths to calculate bond coefficients that were used to quantify the effectiveness of FRC in reducing crack widths. In the beams with steel reinforcing bars, the FRC was found to have little influence on crack widths. In the beams with FRP reinforcing bars, the FRC was found to significantly reduce maximum crack widths.

 

Magazine Title: ACI Structural Journal

 

Title of article:  Crack Width Estimation for Concrete Plates

 

Author: H. Marzouk, M. Hossin, and A. Hussein

 

Issue: May 2010

 

This research is focused on evaluating the crack widths and crack properties of thick two-way slabs and plates used for offshore and nuclear containment structures. The crack width depends on the quantities, orientation, and distribution of reinforcing steel across the crack and characteristics of the bond between the concrete and reinforcement bars in and near the crack. The maximum crack width that is considered acceptable depends on the type of structure, location within the structure, environment, and consequences of excessive cracking.

 

A comprehensive experimental and analytical investigation is presented in this work. The numerical investigation will focus on the available code prediction models for estimating the crack width of concrete plates. The investigation will focus on the suitability of available crack width expressions for thick concrete plates used for offshore concrete structure applications and nuclear containment structures. The experimental work included the investigation of the cracking behavior, such as examining the effect of increasing concrete cover and bar spacing on crack width properties. The crack widths were measured electronically for three series of specimens. The test results were tabulated to compare test results with the available code expressions for calculating crack widths. The tension chord method was modified to predict the crack width for two-way plates under flexural loading.

 

Magazine Title: ACI Structural Journal

 

Title of article:  Comparison of One- and Two-Way Slab Minimum Thickness Provisions in Building Codes and Standards

 

Author: Young Hak Lee and Andrew Scanlon

 

Issue: March 2010

 

 

Minimum thickness provisions for one- and two-way slabs provide a well-established approach for deflection control. Various national design codes and specifications have approached these provisions from different perspectives. Concerns have been raised about the range of the validity of current ACI Code provisions.

 

This paper compares the ACI Code provisions with several national codes and an equation proposed by the authors to incorporate the main design variables affecting deflection control. Based on the results of the comparison, a recommendation is made to adopt the proposed equation, retaining the current values as upper limits.

 

Magazine Title: ACI Structural Journal

Title of article:  Seismic Rehabilitation of Slab-Column Connections

 

Author: Widianto, Oguzhan Bayrak, James O. Jirsa, and Ying Tian

Issue: March 2010

 

Abstract:
The primary focus of the study reported in this paper is seismic rehabilitation of slab-column connections damaged under the application of lateral displacement excursions. Seven 2/3-scale interior slab-column connections were tested to quantify the effects of earthquake damage and the effectiveness of various rehabilitation techniques on repairing seismic-damaged slab-column connections and improving their two-way shear strength. Three alternatives for repairing seismic-damaged slab-column connections were experimentally evaluated: 1) installation of external carbon fiber-reinforced polymer (CFRP) stirrups; 2) application of well anchored CFRP sheets on the tension side of the slab; and 3) installation of steel collars on the column under the slab. All techniques provided a means for repairing seismic-damaged connections and strengthening flat plate structures with inadequate two-way shear capacity. In addition, the installation of the steel collars prevented punching shear failure under the application of simulated seismic displacements and increased the lateral load capacity of non ductile slab-column connections.