Compressive Strength of RC Columns Strengthened with Longitudinal CFRP Composites
Davood
Mostofinejad
author
Niloufar
Moshiri
author
text
article
2013
per
Confining RC columns by FRP composites with fibers oriented in the hoop direction is the most common method of strengthening columns. In the present study, however, the application of CFRP composites with fibers aligned along the column’s axis to improve compressive strength of RC columns has been investigated. Global buckling of composite with longitudinal fibers may result in debonding of FRP from column surface, and thus, the compressive load carrying capacity of the strengthened column would not be increased considerably.
To limit the global buckling of composite under compression, a newly introduced strengthening method, named as Grooving Method (GM), was utilized in the present study and its effect on postponing the buckling of CFRP fibers when aligned along the column axis was investigated. For this purpose, 12 circular RC columns with diameter of 150 mm and height of 500 mm were tested under axial compression. Experimental results showed that while the effect of installing CFRP with conventional EBR method was negligible on the columns’ load capacity, the grooving method considerably enhanced the columns’ maximum loads.
Concrete Research
University of Guilan
2008-4242
6
v.
1
no.
2013
7
18
https://jcr.guilan.ac.ir/article_844_c0439d8b91d1afb0d3f1f32df9f7bc31.pdf
Bending Strengthening of Light Concrete T-Shape Beams Using FRP Sheets
M.K.
Sharbatdar
author
A.
Qods
author
text
article
2013
per
In order to investigate the effect of Composite Fiber Reinforced Polymers (GFRP) on bending strengthening of light weight T-shaped concrete beams in this paper, nine specimens were designed, built and tested. These specimens were divided into A, B & C Groups, according to their conditions and bars arrangement and composite layers. In Group A, beams were designed to have a medium bending defects, while Groups B and C designed for maximum and minimum bending defects.In each group one beam was as reference and the others were strengthened with different numbers of FRP layers.
According to observations and results, flexural strength increase of in Group A was from 81% to 116% while that was from 33% to 208% in Group B and 67% to 100% in Group C. And also the effect of using stronger epoxy and anti-slipt material to change shear failure (debonding) to flexural debonding and increasing strength was investigated in this paper.
Concrete Research
University of Guilan
2008-4242
6
v.
1
no.
2013
19
33
https://jcr.guilan.ac.ir/article_845_316752ae0059f8bb43cfa2027242bd80.pdf
Behavior of Reinforced Concrete Frames Braced with a Combination of X and knee Bracing
F.
Rezaie
author
Sh.
Jafari Radniya
author
text
article
2013
per
In this study, 4 and 8 story reinforced concrete frames retrofitted with X and Knee bracing systems using SAP2000 V14 software and nonlinear static analysis. Then the behavior of these two systems are compared with each other and according to standard 2800 requirements, X-bracing system are located on the lower stories. Static analysis is performed using a uniform and triangular load patterns. Nonlinear plastic hinges have been assigned to the each seismic elements (beams and columns of moment resisting frame, steel bracing and knee elements). Models are chosen such that the participation of moment frame columns and steel bracing in different models have varied. The results indicate that in the X-braced reinforced concrete frames, large tensile forces are applied to the adjacent columns of steel bracing, especially in the lower stories. This problem cause forming plastic hinges in the columns. Also, reinforced concrete frames with knee bracing have the low strength and stiffness, while it is not always more ductile than X bracing. In this research combination of two systems, X and knee bracing, at the height indicate a bracing system that has desirable features of two bracing systems simultaneously and disadvantages of each system can be modified by the other.
Concrete Research
University of Guilan
2008-4242
6
v.
1
no.
2013
35
52
https://jcr.guilan.ac.ir/article_846_8667acf5c993c8e60aee3832106582a5.pdf
Combined Effect of Silica Fume and Zeolite on The Fresh and Hardened Properties of Self-Compacted Concrete
R.
Madandoust
author
M. M.
Ranjbar
author
S.Y.
Mousavi
author
text
article
2013
per
The usages of different additions as a cement replacement in the production of self-compacted concrete (SSC) can lead to a lower material cost, lower environmental pollution, energy consumption and recycling by-product materials. Although, the inclusion of additions may enhance certain properties of SCC, the others may be worsening. To overcome this problem, the combined use of the additions has been recently recommended by researchers. In this respect, the main objective of the present study is to investigate the fresh and hardened properties of SCC made with binary and ternary cementitious blends of silica fume and zeolite. Fresh properties of SCC will be examined by slump flow, visual stability index, T50, V-funnel, L-box and sieve segregation resistance tests. The hardened properties were tested for compressive strength (at different ages), splitting tensile strength, initial and final absorption. To simulate the real-world applications, slump flow and compressive strength changes with hauling time were also considered.
The fresh concrete test results revealed that by substituting optimum levels of silica fume and zeolite in SCC, satisfactory workability and rheological properties can be achieved. Silica fume inclusion enhanced both early ages and long-term strength of SCC with zeolite. Moreover, reduction in the slump flow retention of the SCC mixtures containing zeolite was compensated by using silica fume.
Concrete Research
University of Guilan
2008-4242
6
v.
1
no.
2013
53
71
https://jcr.guilan.ac.ir/article_847_c77ac96d6f8e929d4568c20467adce9a.pdf
Evaluation of Fiber Reinforced Concrete Containing Recycled Concrete Aggregates with Non-Destructive Methods
A.
Sadrmomtazi
author
H.
nosrati
author
M.H.
Tahmouresi
author
text
article
2013
per
The use of concrete in the construction industry is growing day by day. Due to the limited life span of concrete structures and also the destruction of concrete structures by natural factors such as earthquakes, floods, hurricanes and ... we will always faced with massive amounts of waste concrete that will cause environmental damages. On the other hand natural resources are also limited for generating aggregates that in near future we should use waste concretes as recycled concrete aggregates for an alternative of natural aggregates to save the natural resources. In this study, the replacement proportion of fine and coarse recycled concrete aggregates with conventional aggregates, is the similar percentages of 0, 25, 50, 75 and 100%, which will include 5 mixing design. With increased use of recycled concrete aggregate, reduction of recycled concrete properties, a increase in water absorption and decrease in slump concrete can be observed that it has been tried to compensate this loss in the slump by using super plasticizer. In order to improve the engineering properties of recycled concrete and Study the Effect of polypropylene fibers on the properties of recycled concrete, the polypropylene fibers with the length of 6 mm and different volume percentages of 0.1, 0.2 and 0.3 percent were used that formed of 15 mixing design. In this study, the Compressive strength, Drying shrinkage, Water absorption, Ultrasonic pulse velocity, Electrical strength and SEM tests were done on the samples. withIncrease in the mass percentage ofpolypropylene fibersin recycledconcretes, decrease in results ofUltrasonic pula velocity and Water absorption, increase in Electrical strength results and alsonegativeeffectsonthe compressive strength have been observed. Interms of0.1 % by volume of polypropylenefibersinconcretedesign, Drying shrinkage improvedbutwith using 0.2and0.3 % by volume ofpolypropylenefibers, the Drying shrinkage increasedComparedwithsampleswithnofibers.
Concrete Research
University of Guilan
2008-4242
6
v.
1
no.
2013
73
86
https://jcr.guilan.ac.ir/article_849_1e655d2d1ea302859ef9c1c951c240a1.pdf
A New Method of Mix Design for Self-Consolidating Concrete Based on Compressive Strength
A.K.
Shirzadi Javid
author
B.
Rahmati
author
text
article
2013
per
Self- consolidating concrete (SCC) mix design should consider the appropriate characteristics in terms of workability, rheology, strength and durability simultaneously. Because of this, already standard method in the world for SCC mix design has not been expressed. In this paper, a new method of SCC mix design based on compressive strength is presented. various parameters such as aggregate gradation, packing density, volumetric ratio of water to powder, water to cement ratio, 28-day compressive strength is considered. Results of mix designs made in the laboratory are perfectly accordant with the values of target, so the proposed method is a real and valid.
Concrete Research
University of Guilan
2008-4242
6
v.
1
no.
2013
87
102
https://jcr.guilan.ac.ir/article_848_d110aab609b3bb3232f4029cc2dd51ce.pdf
Investigating the Effect of Using Macro and Micro Steel Fibers with Nano Silica on the Mechanical Properties of Concrete
J.
Esmaili
author
A.
Mohamad Jafari
author
text
article
2013
per
Using fibers with different sizes and types part plays more important roles in energy absorption capability of reinforced concrete structures. The effects of different sizes and proportions of fibers on energy absorption capability, bending strength, tensile and compressive strength of concrete have been investigated in this work. Steel fibers have been used to improve the post fracture behavior of concrete and pozzolanic materials have been added to concrete to increase the strength of transition zone. In this regard, the combination of fibers in different sizes for bridging the cracks at different stages of the crack growth and also using nano silica with high surface energy and reactivity can be considered. Simultaneous use of mentioned additives can improve the properties of concrete in the case of using appropriate mix design. Different mix designs containing combinations of different types of steel fibers and micro silica and nano silica have been tested and an optimized mix design of concrete with improved mechanical properties has been reached. Energy absorption capability, bending strength, tensile and compressive strengths can be mentioned as those mechanical properties.
Concrete Research
University of Guilan
2008-4242
6
v.
1
no.
2013
103
114
https://jcr.guilan.ac.ir/article_842_8cbbb55dc3792bf40564b5d0950f23ad.pdf
The Effects of Polypropylene Fibers on Mechanical Properties and Permeability of Concrete
A.
Foroughi-Asl
author
F.
Hoseinnejad
author
text
article
2013
per
In recent years, using of various fibers in concrete mix is growing and each type creates some specific property in concrete. Polypropylene (PP) fiber is a new type fiber with significant advantages in mechanical properties of fibrous concrete. In this research two series of concrete mix were made ( without fibers - control concrete - and with PP fibers in length of 6 and 12 mm and in 0.2, o.4, and o.8 percent of cement content) by local aggregates(sand and gravel), Portland cement, silica fume (as pozzolan), and superplasticizer (as admixture with polycarboxilic base). The specimens were cured for 3, 7 and 28 days and tested for compressive and flexural strength. The specimens elected for measuring the permeability depth were tested under 5 atm. water head after 28 days curing and permeability index was calculated by Valenta equation. Results showed that early compressive strength of fiberous specimens was less than control specimens but by increasing the age of specimens, the strength will be increased and maximum compressive strength was for 28-d specimen with 0.8 percent of PP fiber but the flexural strength of fibrous specimens were more than normal specimens at all ages and the maximum flexural strength was for 28-d specimen with 0.4 percent of PP fiber. Permeability of fibrous specimens was less than normal specimens and the minimum value belongs to specimen with 0.4 percent of PP fiber.
Concrete Research
University of Guilan
2008-4242
6
v.
1
no.
2013
115
125
https://jcr.guilan.ac.ir/article_843_602dfafeefa3fbc44987f8c675b9c332.pdf