Crack Resistance of the Self-Stressed Members Reinforced with FRP Bars

Abstract

Fiber reinforced polymer (FRP) bars are widely used in building structures, especially that are exposed to the aggressive environment influence and other special conditions. Nevertheless, due to the low FRP (e.g. glass, basalt, aramid fibers reinforced polymers) bars modulus of elasticity, exceeding crack opening width, as well as deflections can be observed. FRP bars pretensioning is considered as an effective method of its structural performance increasing. Physico-chemical method of the FRP bars pretensioning based on the self-stressing concrete utilizing is an alternative to the mechanical method and in its turn doesn’t need for special devices and anchorage systems as well as qualified personnel. Assessment of the initial stress-strain state obtained during self-stressing concrete expansion stage in the reinforced self-stressed members is presented. Diagram method of the self-stressing parameters verification based on the static loading tests results is presented. Comparison of the initial stress-strain state obtained during concrete expansion stage and predicted by the proposed model, as well as assessment of its influence on the behavior at the static loading stage in cases of the self-stressed reinforced with FRP bars members and traditionally reinforced with steel bars self-stressed members was performed.

Некоторые Замечания О Химическом Предварительном Напряжении Арматуры Из Напрягающего Бетона

“…Intensive development of the Portland cement concrete technology in the last decades allowed to obtain high-performance concrete (HPC) or even ultra-high performance concrete (UHPC) with a compressive strength above 120 MPa. Nevertheless, the inadequate ratio of any concretes compressive to tensile strength (as it was stated in our works [15][16][17], concretes of the new generation are still artificial stones with good performance under compression-only). Low tensile strength in combination with inherent to concrete early-age and long-term effects (autogenous as well as drying shrinkage, creep, temperature) lead to decreasing of the serviceability parameters of concrete structures.…”

“…I think today it is the most progressive and perspective model for early-age self-stressing concrete strain/stress assessment. Some modification of this model for self-stressing concrete with high energy of expansion presents in our works [15][16][17].…”

Influence of the initial prestressing on the crack resistance of the self-stressed members reinforced with steel and FRP bars

“…Beams initial restrained expansion curvature values obtained on the basis of measured restrained strains varied in the diapason (1,16-1,82)•10 -5 mm -1 . These values of the beams initial restrained expansion curvature obtained at the self-stressing stage should be considered as a result of two developed in time superposed basic processes: on one handself-stressing concrete expansion in non-symmetrical restraint conditions and on the other handconcrete elastic compressive strains accumulating under monotonically increasing in time restraint reaction [1,5,6]. At the same time so-called beam initial «elastic» curvature (that is determined from the accumulated concrete elastic compressive strains distribution) only have an influence on the self-stressed member behaviour under the applied static load in terms of traditional decompression.…”

“…Test results obtained within loading of the selfstressed beams are presented in Table 6 and Table 7. (1) 34 (6,8) 108 (21,6) «B» I-BECS- (2) 37,3 (6,5) 120 (21,0) I-BECS- (3) 39,5 (6,9) 120 (21,0) I-BECS- (4) 46,6 (8,2) 125,4 (22,0) II-BECF- (1) 40,5 (8,1) 150 (30,0) «Sh» II-BECF- (2) 43,5 (8,7) 130 (26,0) II-BECF- (3) 39,0 (7,8) 150 (30,0)…”

“…Analysis of the numerous scientific papers [3,4] in the field of the self-stressed structures has shown that such a members were investigated mainly on the concrete restrained expansion stage and only a limited data presents theoretical and experimental results about such a members (conventionally reinforced with steel bars) resistance under the loading. As it was pointed in [5,6] because of the FRP low (close to the concrete) modulus of elasticity, FRP reinforcing bars can be effectively utilized with initial pretensioning only. Physico-chemical pretensioning of such a bars with self-stressing concrete can be considered as an effective method of the member prestressing.…”