Strength of reinforced-concrete hydraulic structures having block joints

Abstract

Operating experience and results of on-slte observations of the work of reinforcedconcrete hydraulic structures (such as locks, retaining walls, abutments) show deviations in behavior from the calculated assumptions, expressed in more intense cracking and increased deformation, which ultimately indicates a decrease of bearing capacity [6,7]. Examples are the wall of the No. 2 lock of the Moscow Canal [7], retaining walls of the Plyavinyas hydroelectric station, the results of'testing a large-scale model of the lock of the Votklnsk hydroelectric station at the testing station of the B. E. Vedeneev All-Unlon Sclentific-Research Institute of Hydraulic Engineering (VNIIG) [9], and abutment of the Khantalka hydroelectric station. In a number of cases costly repair works to strengthen the structures were required.The cause is the inaccurate prediction of external effects and resistance to them of the reinforced-concrete structure experlenclng the combined effect of the bending moment and transverse forces [8].

Improvement of the method of calculating the strength of inclined sections in massive reinforced-concrete structural elements

“…the horizontal crack along the longitudinal reinforcement in the direction from the joint to the support [4] formed before breaking of the beams: at a smaller length of the zone of separation of the reinforcement band than in monolithic beams. Thus the longitudinal reinforcement hardly increased its flexibility due to the formation of a zone of separation of the reinforcement band right up to breaking of the beams.…”

“…

When designing massive reinforced-concrete structural elements of hydraulic structures it is necessary to take into account a variety of factors affecting the strength of inclined sections for the purpose of rational reinforcement of the elements and provision of their rel~ability.The method in the construction specifications and regulations SNiP II-56-77 "Concrete and Reinforced-Concrete Structural Elements of Hydraulic Structures.Design Standards" for calculating the strength of inclined sections does not take into account one of the main factors characteristic of massive reinforced-concrete elements, nomely, the presence of construction joints and their effect on strength, which can lead to insufficient reliability of the structures or to an unwarranted factor of safety (superfluous use of reinforcement).Investigations [1][2][3][4][5][6] carried out at the research department of the A11-Unlon Planning, Surveying, and Sclentlflc-Research Institute (Gidroproekt) made it possible to accumulate a considerable volume of data on the behvaior of relnforced-concrete elements with construction joints: to determine the design requirements with respect to the rational arrangement of joints for which the elements behave analogously to monolithic elements and arrangement of joints for which a substantlal decrease of strength occurs compared to monollthlc elements [6]. The developed method of calculatlng the strength of Incllned sections is based on conslderatlon of the combined stress of concrete in the compressed zone by strength theory [3,4]

where Qcb is the transverse force absorbed by concrete of the compressed zone in the dangerous section; Qrb is the transverse force absorbed by the longitudinal reinforcement in the section along the contruction Joint.

The method of dete~ining the transverse force Qcb is based on integration of the shear stresses Txy over height of the compressed zone of concrete xo [I, 2]

where ~ ffi (80--R)/100; ax and os are respectively the principle compressive and tensile stresses, which are functions of the normal compressive ox, tensile Oy, and shear Xxy stresses [2].

…”

“…The developed method of calculatlng the strength of Incllned sections is based on conslderatlon of the combined stress of concrete in the compressed zone by strength theory [3,4] where Qcb is the transverse force absorbed by concrete of the compressed zone in the dangerous section; Qrb is the transverse force absorbed by the longitudinal reinforcement in the section along the contruction Joint.The method of dete~ining the transverse force Qcb is based on integration of the shear stresses Txy over height of the compressed zone of concrete xo [I, 2] where ~ ffi (80--R)/100; ax and os are respectively the principle compressive and tensile stresses, which are functions of the normal compressive ox, tensile Oy, and shear Xxy stresses [2]. …”