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Showing 1-5 of 125 Abstracts search results

Document: 

SP327-12

Date: 

November 1, 2018

Author(s):

Nancy Torres, Gustavo Tumialan, and Camilo Vega

Publication:

Symposium Papers

Volume:

327

Abstract:

In order to ensure a continuous and reliable path for the lateral loads caused by earthquake or wind forces, FRP-strengthened masonry walls that are part of the lateral load resisting system of a building require the joint work of the FRP strengthening to resist tensile stresses in the masonry and anchorage to the boundary structural elements (foundations or beams) to transfer the loads. This article presents the results of an investigation on the assessment of anchorage methods and FRP strengthening configurations for unreinforced masonry (URM) walls subjected to in-plane loads. Fourteen masonry walls were constructed for this experimental program. All of the walls were built with hollow clay bricks, typical of URM structures in Colombia and other parts of the world. The specimens for this investigation included slender and squat walls. The dimensions of the slender walls were 1.20 m. [4 ft] long, 1.90 m. [6.2 ft.] high, and 120 mm [4.8 in.] thick. The dimensions of the squat walls: 2.50 m. [8.2 ft.] long, 1.90 m. [6.2 ft.] high, and 120 mm [4.8 in.] thick. The walls were strengthened using two configurations: (1) Layout ‘H’ involving horizontal CFRP laminates along on wall side, and vertical CFRP laminates at each wall toe on one side of the wall, and (20 Layout ‘X’ involving diagonal CFRP laminates oriented at approximately 45 degrees on one side of the wall. Four anchor systems were evaluated: (1) System 1 (CFRP anchors embedded in the base beam), (2) System 2 (CFRP bonded to the base beam), (3) System 3 (FRP bonded to grout blocks), and (4) System 4 (FRP wrapped around grout blocks). The walls were tested in two series: (1) Series 1 – Monotonic Loading, and (2) Series 2 – Cyclic Loading. The test results demonstrated that Anchor System 4 was the most effective anchorage system. The walls strengthened with Anchor System 4 failed due to rupture of the CFRP laminates wrapped around the grout block. In general, the largest increases in in-plane capacity, when compared to the control walls, were observed in the slender walls. The walls with the ‘H’ Layout showed more ductility and less degradation of the lateral stiffness than the walls strengthened with the ‘X’ Layout.


Document: 

SP327-32

Date: 

November 1, 2018

Author(s):

Zuhair A. Al-Jaberi, John J. Myers and Mohamed A. ElGawady

Publication:

Symposium Papers

Volume:

327

Abstract:

There are large numbers of existing buildings around the world and in North America especially in California have been constructed with reinforced masonry since 1930s. These old reinforced masonry walls have not been improved to meet the current standards. Current ACI 440.7R reported as Guide for Design & Construction of externally bonded FRP System for Strengthening Unreinforced Masonry Structures. This document does not address strengthening of existing reinforced masonry structures (i.e. with steel reinforcement). The principle objective of this study was to determine and discuss the failure mechanism as well as to investigate the flexural behavior of reinforced masonry walls strengthened with externally bonded system and subjected to out-of-plane cyclic loading. This will be evaluated by comparing the flexural capacity and ability to sustain large deflection of specimens strengthened with different strengthening systems. In addition, the effect of specific parameters on the flexural response of reinforced masonry wall was investigated including: type and amount of fiber and masonry bond pattern. This study aimed to develop a database of experimental test results to validate the design model presented in next version of ACI 440.7R document. The performance of twelve strengthened masonry specimens was investigated. The strengthening systems that used in this study are fiber reinforced cementitious matrix (FRCM) and fiber reinforced polymer (FRP) technique. These simply supported walls were tested in four-point bending with an effective span of 1.12 m (44-in.) between the supports under an out-of-plane cyclic load at a rate 1.27 mm/min (0.05-in./min). The test results indicated that the flexural behavior of reinforced masonry walls strengthened externally by FRP may be controlled by either FRP rupture or debonding (intermediate crack or plate end debonding failure). The flexural behavior of reinforced masonry walls strengthened externally by FRCM may be controlled by either fiber slippage or debonding.


Document: 

SP327-22

Date: 

November 1, 2018

Author(s):

Gustavo Tumialan, Nancy Torres, Alfonso Quintana, and Antonio Nanni

Publication:

Symposium Papers

Volume:

327

Abstract:

This article presents the results of a research program on the behavior of masonry walls reinforced with FRP bars subjected to out-of-plane loads. The article also proposes a preliminary protocol for the flexural design of masonry walls reinforced with FRP bars. The objectives of this investigation were: (1) evaluate the flexural behavior of masonry walls reinforced with FRP bars subjected to out-of-plane loads, and (2) develop preliminary design recommendations. Ten masonry walls, 2 m [6.6 ft] high, were subjected to out-of-plane loads, tested under quasi-static loading cycles. The test specimens included walls constructed using concrete and clay masonry units, reinforced with Glass FRP (GFRP) and Carbon FRP (CFRP) bars in different configurations. All the FRPreinforced masonry walls showed a bilinear moment-deflection curve with one steep slope up to cracking of masonry and a decrease in stiffness after cracking. The majority of the walls failed due to crushing of masonry in the compression side. After failure occurred and as the out-of-plane load was progressively removed, the walls returned to a position close to the initial vertical position. In general, the approaches used to calculate flexural strengths and deflections provided good agreement with the experimental results.


Document: 

SP327-38

Date: 

November 1, 2018

Author(s):

Cristian Sabau, Cosmin Popescu, Gabriel Sas, Thomas Blanksvärd and Björn Täljsten

Publication:

Symposium Papers

Volume:

327

Abstract:

This paper summarizes the state-of-the-art on the topic of structural wall panels strengthened using fabric reinforced cementitious matrix composites (FRCM) composites. A systematic review of the literature is carried out to identify gaps in the available literature. A database of experimental tests, relevant for structural panels, was created and used to assess the influence of parameters such as test method, fiber type and material compressive strength, on the performance of FRCM strengthening. Since experimental investigations on walls strengthened with FRCM composites is still limited and mostly focused on shear, further investigations on walls as compression members can be considered timely, especially walls with openings, which have been overlooked. Experimental tests performed by the authors on reinforced concrete walls with openings are presented and assessed relative to the complete database. It was shown that FRCM composites are suitable repair solutions when new openings need to be created in existing walls.


Document: 

SP-330-10

Date: 

September 26, 2018

Author(s):

Luigi Coppola, Denny Coffetti, and Elena Crotti

Publication:

Symposium Papers

Volume:

330

Abstract:

Since replacement of portland cement by other cementations materials is one of the main strategies to reduce the environmental impact of cementitious mixture, several innovative portland-free binders have been investigated. This paper is aimed to study a ground granulated blast furnace slag (precursor) activated with a mixture in powder form (activator) of sodium metasilicate pentahydrate, potassium hydroxide and sodium carbonate to manufacture portland-free mortars for conservation, restoration and retrofitting of existing masonry buildings and concrete structures. Several activator/precursor combinations (2%-32% by mass) were used to investigate the effect of alkali activation on the rheological, elastic and physical performances of repair mortars. The experimental data show that by changing the activator/precursor combination it is possible to “tailor” the 28-day compressive strength of the mortar. The activator dosage represents the key parameter influencing not only mechanical performance but also the hydraulic shrinkage: the higher the activator dosage, the more pronounced the mortar shrinkage. Shrinkage values for alkali-activated mortars (AAM) are significantly higher (2000 – 4000 ∙ 10-6) compared with those of cement-based mortars with the same compressive strength. Consequently, a reduction of shrinkage by means of shrinkage reducing (SRA) and/or water retention admixtures is necessary. However, although shrinkage is very high, the modulus of elasticity is about 40% lower than that of a portland cement mortar of the same strength level. On the basis of the experimental data AAMs seem to be more promising for a sustainable future in construction since the GER (Gross Energy Requirement) and GWP (Global Warming Potential) are dramatically reduced by 80 - 90% and 70 - 80%, respectively compared with traditional portland cement mortars with the same compressive strength.


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