Strengthening of Reinforced Concrete Beams Subjected to Concentrated Loads Using Externally Bonded Fiber Composite Materials

Abstract

Renovation, restoration, remodeling, refurbishment, and the retrofitting of buildings often imply applying forces (i.e., concentrated loads) to beams that before were subjected to distributed loads only. In the case of reinforced concrete structures, the new condition causes a beam to bear a concentrated load with the crack pattern that resulted from the distributed loads which had acted before. If the concentrated load is applied at or near the beam’s midspan, the new shear demand reaches the maximum where cracks are vertical or quasi-vertical, and where inclined bars are not common according to any standards. So, the actual shear capacity can be substantially lower than new shear demand due to the concentrated load. This paper focuses on reinforced concrete beams whose load distribution has to be changed from distributed to concentrated and presents a design method to bring the beam’s shear capacity up to the new demand. The method consists of applying fiber composites (fiber-reinforced polymers or fiber-reinforced cementitious material) with fibers at an angle of 45° bonded to the beam’s web. This kind of external reinforcement arrangement has to comply with some practical measures, which are presented as well. The paper also provides the analytical model that predicts the concentrated load-carrying capacity of a beam in the strengthened state. The model accounts for the crack’s verticality, which nullifies the contributions of steel stirrups, aggregate interlock, and dowel action, and for the effective bond length of each fiber, which depends on the distance between the ends of the fiber and the crack it crosses.

Theoretical and Experimental Substantiation of the Efficiency of Combined-Reinforced Glass Fiber Polymer Composite Concrete Elements in Bending

“…Our results showed a higher bearing capacity and especially in combination with the fact that the mass of our elements is less than sim- Next, consider the constructive effect we have achieved, it consists of improving the performance of an improved design due to the synergistic effect of fiber reinforcement of bending elements and in combination of such dispersed reinforcement with polymer composite reinforcement with rods. In this regard, our results seem to be effective in comparison with the results of the authors [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Our results showed a higher bearing capacity and especially in combination with the fact that the mass of our elements is less than similar reinforced concrete elements.…”

“…Next, consider the constructive effect we have achieved, it consists of improving the performance of an improved design due to the synergistic effect of fiber reinforcement of bending elements and in combination of such dispersed reinforcement with polymer composite reinforcement with rods. In this regard, our results seem to be effective in comparison with the results of the authors [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Our results showed a higher bearing capacity and especially in combination with the fact that the mass of our elements is less than sim- Next, consider the constructive effect we have achieved, it consists of improving the performance of an improved design due to the synergistic effect of fiber reinforcement of bending elements and in combination of such dispersed reinforcement with polymer composite reinforcement with rods.…”

“…All this is proposed for use not only in compressed elements, as in [18,19,[28][29][30][31][32][33], but, of course, in tensioned bending elements, which emphasizes the more rational operation of fiber-reinforced elements, since fiber reinforcement is primarily directed for bending and tensile loads. In this regard, our result surpasses the results of [6,9,14,17,18,27,[33][34][35][36][37][38].…”

“…The improvement of reinforced concrete bending elements is the most relevant at the present time and has already been considered in many studies, for example, in [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. In this case, various improvement methods are used: reinforcement with polymer composite materials [2,5,8,[10][11][12][13]15,16], various fibrous materials [6,9,14], Fe-SMA activation [3], and cathode-ray tubes made of glass waste [7]. The economic aspect was also considered-the cost of reinforced concrete beams largely depends on the brand of reinforcing steel [1].…”

“…Research on improving the characteristics and operation parameters of compressed [18,19,[28][29][30][31][32][33] and bending elements [6,9,14,17,18,27,[33][34][35][36][37][38] because of fiber reinforcement continues to expand and open new possibilities for their application. At the same time, researchers have studied the behavior of columns and beams made of steel fiber concrete [6,30], ultrahigh strength fiber concrete [36], glass geopolymer concrete with hybrid fibers [29], steel fibers [34,35], basalt fibers [34], hybrid epoxy resin, reinforced with flax or fiberglass [28], and steel fibers from scrap tires [31].…”