RESEARCH STRENGTH OF INDIRECTLY-REINFORCED BEAMS ON AN INCLINED CROSS-SECTION PRODUCED BY LLP “BINOM”

E. Seidullayev, K. Ermuhanov

Currently, the indirect reinforcement of concrete is mainly used to increase the strength of the compressed elements with concentrated loads of action (local compression of the end cap columns near the joints, anchoring zone pre stressed reinforcement). The contribution of indirect reinforcement to increase the bearing capacity of the element is evaluated given concrete compressive strength, defined by the formula (48) SNIP 2.03.01-84 *.

The aim of our experiments was to determine the effect of lateral reinforcement for the maximum transverse force perceived bendable concrete elements on the inclined cross-section at their destruction. To achieve this goal it was necessary to achieve the following objectives: to develop a test method; perform tests of prototypes with different percentages of indirect reinforcement for the determination of the maximum lateral force and indirect contribution to the reinforcement of load-bearing capacity; identify the features of the effect of lateral reinforcement in the elements of the value of the bearing capacity and the nature and form of the destruction of the inclined sections; experimental set limit transverse force perceived bendable concrete elements on the inclined cross-section, at various ratios of lateral reinforcement.

Test samples were divided into 2 groups for the study of the various factors influencing the marginal transverse force perceived sloping sections. The first group consists of two cross members - the twins (TAA TAA-1.1 and-1.2) with a transverse reinforcement - grids with a pitch of 70 mm in the form of wire mesh package of Ø3Vr-I and Ø4Vr-I. In the second group also ravine - the twins (TAA TAA-2.1 and-2.2) with a transverse reinforcement grids as a package with a pitch of 50 mm wire Ø3Vr-I and Ø4Vr-I. In all samples the stretched zone reinforced rods 2Ø12 A-III. Dimensions prototypes (Table) were due to the limitations of the test equipment availability. The objectives of the research group 1 is to get the results of the indirect effect of reinforcement on the bearing capacity of the inclined cross-section of the joint action of the bending moment M and shear force Q. The objectives of the research group 2 are to get the results of the effect of lateral reinforcement on the strength of an inclined cross-section by the action in the main transverse force Q. In samples (with the subscript "a"), the transverse reinforcement in the form of grids is substituted minor diameter C-2 provided in the zone of formation of cracks inclined bent elements.

Grids lateral reinforcement can be welded of the intersecting rods, while on the requirements of building regulations must observe the following conditions: a) cross-sectional area of rods (wire) grid on the unit of length in one direction and the other should not differ by more than 1.5 times; b) a step grid (distance between the grids in the axes of the rods in one direction) are taken at no more than 1.3 of the element section and not more than 150mm; c) in the grid mesh size assigns light at less than 1.4 of the element section, and not more than 100mm.

To prevent the destruction of the inclined sections of the action of the time and on the support for reliable anchorage of longitudinal reinforcement to them were welded cross bars with 10mm diameter 5cm step in the area of the anchorage.

The prototype test was carried out according to the scheme of four - point and three-point bending. Before tests on each beam installed cargo distribution plate 75x150x10mm. Driving test major series of beams is shown in Fig. 1, a general view of the experimental setup in Fig. 2. In all the basic series to prevent the influence of the two thrust bearings were adopted hinge-movable.

In tests of all samples was used the equipment brand "ZIM" (type: R-50, GOST 8905-93). The app load was carried out in steps of 15-20kN, which corresponded to 1/5 (20%) of the projected breaking force. The magnitude of the load is controlled by indications silo meters corresponding test equipment.

Sample mark	b	R	Rb	Rbt		Driving test	F^exp	F^снип	F^exp/ F^снип
ТАА-1.1 ТАА-1.1а	75х150х135	В26.4	21.05	2.06	0,0180		76,8 68,1	64,48 58,81	1,191 1,158
ТАА-1.2 ТАА-1.2а					0,0102		76,53 67,4	64,48 58,81	1,187 1,146
ТАА-2.1 ТАА-2.1а					0,0252		109,4	90,21	1,213
							87,6	74,5	1,176
ТАА-2.2 ТАА-2.2а					0,0142		108,8	90,21	1,206
							86,9	74,5	1,168

The sequence of formation of cracks in all test samples was essentially the same: first, in the tension zone of the beams appeared normal - torque, then inclined crack of shear force. The development of cracks as loading and forms of destruction of samples vary greatly depending on the percentage of transverse reinforcement. Along with common features, each group of prototypes and were especially fissures of transmitted load and the nature of the forms of destruction.

The destruction of all the samples as expected, did not differ from the destruction of the inclined beam cross section under the action of concentrated loads, ie, identical as in earlier experiments conducted by other authors. The final destruction of the sample came with large opening inclined cracks. Dependence of the strength on the inclined cross-section of the lateral reinforcement ratio is shown in the figure:

Fig.2. The dependence of the strength on the inclined cross-section of the lateral reinforcement ratio

Based on the results of the pilot study, the following conclusions:

1. Indirect reinforcement at the reference length (s) of the span bent elements (ie replacement clamps on the grid of small diameter), resulting in a substantial increase in the bearing capacity of the inclined cross-section of the joint action of the moment and shear force.

2. Indirect reinforcing a positive impact on the strength of compressed concrete zone, ie, increases given prism strength of concrete compressed zone of the inclined crack of a flexible element.

REFERENCES:

1. Zalesov A.S., Klimov Y.A. Durability of reinforced concrete structures under the action of shear forces. Kiev. : Budivelnyk, 1989.-241p:. Il.

2. Innovative patent №27350. Reinforcing cage of reinforced concrete products (auth. Ermuhanov K.E., Shekeev D.B.).

3. Shekeev D.B. The strength of concrete beams on an inclined section. Magist. thesis on competition of acad. Master degree of tehn. sciences at M. Kh. Dulatiy TarSU,: Taraz, 2015.

4. GOST 14098-91 Welded joints of reinforcement and inserts manufacturing of reinforced concrete structures. Types, design and dimensions.