Strengthening of ferrocement beams in torsion, using CFRP

Dissertant

al-Ubaydi, Asil Sami

Thesis advisor

Sarsam, Qays Fuad
Abd al-Karim, Ala K.

University

University of Technology

Faculty

-

Department

Department of Building and Construction Engineering

University Country

Iraq

Degree

Master

Degree Date

2012

English Abstract

Ferrocement is a type of thin reinforced concrete made of cement-sand matrix with closely spaced relatively small diameter wire meshes, with or without steel bars of small diameters called skeletal steel.

Torsion is resisted well by closed form reinforcement, due to the circulatory nature of the torsion inducing shear flow stresses in a beam.

Therefore, it will be more efficient to have strengthening schemes, which are wrapped in closed form around the cross section.

The main aim of the present investigation is to study the behavior of ferrocement beams strengthened with carbon fiber reinforced polymer (CFRP) as strips under pure torsion.

Variables considered in the test program include: Number of wire mesh units, (2, 3, 4) units, where a unit consists of two layers of wire mesh with skeletal steel.

Compressive strength of concrete, using two mixes (1:1.5 ,1:2 ) with superplasticizer .

Spacing of CFRP strips, (100,160,200) mm c/c.

The experimental work includes an investigation of 24 rectangular beam specimens cast, strengthened and tested under pure torsion.

The cross-sectional dimensions of the specimens were rectangular (50 mm width , 120 mm height, and 1 m length).

24 beams (six groups) were divided and made in two different mixes.

Three groups from the same mix had different reinforcement of units (wire mesh layers).

Also, four beams from each group had different spacing of CFRP strips [one beam without CFRP(reference beam), and three beams with CFRP at different spacing].

The behavior of specimens was monitored by reading the loads, vertical and horizontal displacements at the two ends (to calculate the rotations), and observing the crack patterns.

Test results are discussed based on torque – rotation behavior, beam elongations, and influence of parameters on ultimate torque and failure modes.

An empirical expression is proposed in this work.

This expression is obtained by carrying out a regression analysis of 24 ferrocement beams based on using Data fit 8.2 computer program.

In addition, design charts are proposed.

The experimental results indicate that using optimum dosage of superplasticizer(1.4 % of weight of cement) improved the compressive strength values of mortar at (65.65, 61.53) MPa.

With this result, the produced mortar is similar to HSC(High Strength Concrete).

Also, increasing compressive strength by (6.70 %) leads to total average increase in ultimate torque by (16 %).

For the 1:1.5 mix, increasing the number of units from 2 to 4(reinforcement near the surface of beam section) led to increased ultimate torque by (13.44 %) and from 2 to 3(uniformly distributed reinforcement) led to increases in the ultimate torque by only (3.24 %).

Similarly for the 1:2 mix the ultimate strength was (14.67 %) (2 versus 4), while it was (3.97 %) (2 versus 3).

The reinforcement near the surface will be more efficient.

When the beams are strengthened with CFRP strips, the lowest and highest increase in torque is at 112 % (4- units,@200 spacing) and 312 % (4-units,@100 spacing), respectively for 1:1.5 mix and 104.55 % (4-units, @200 spacing) and 300 % (4- units,@100 spacing), respectively for 1:2 mix when compared with reference beams.

The ultimate torque of beams with CFRP strips @ 100 mm and 160 mm is greater than beams with CFRP strips @ 200 mm by (95.56 %,51.11 %), respectively for the group having 4-units.

Decreasing the spacing of CFRP led to decreasing elongation of beams between (19 % to 37.52 %) depending on the compressive strength and number of units.

Application of an empirical expression leads to a good estimation for the ultimate torque for all the beams, despite neglecting the effect of skeletal steel.

The lowest ratio of experimental torque to the calculated torque is 0.904, while the mean value of these ratios is equal to 1.028.

This equation leads to a COV of (9.24 %) for the ratio Tutest / Tucal.

and giving a coefficient of multiple determination (R2)= 95.45672.

Main Subjects

Engineering & Technology Sciences (Multidisciplinary)

Topics

• Building materials
• Concrete
• Mechanics
• Reinforced concrete

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-418855