Residual Bearing Capacity Research Articles

EXPERIMENTAL STUDY ON BEARING CAPACITY OF DANGEROUS AND/OR OLD PRE-STRESSED CONCRETE BOX GIRDERS

In order to obtain the true bearing capacity of dangerous and old pre-stressed concrete box girder bridges, experiments on flexural and shear bearing capacity of full-scale dangerous and old pre-stressed concrete small box girders are conducted to study the mechanical degradation behavior of dangerous and old pre-stressed concrete box girders. Through the residual bearing capacity test of the full-scale prefabricated box girder, the load, deflection, strain and crack width of the test girders are measured and analyzed. The residual bending and shear ultimate capacity and stiffness of the small box girders are analyzed. The bending and shear behavior and failure mechanism of precast box girders in danger are obtained. The comparisons between the results of full-scale test and the calculated value of bearing capacity and also the design value of the internal force of I-Class highway are operated to analyze the actual performance of the small box girder made of dilapidated concrete. The damage reduction coefficient is introduced to establish the formula of ultimate bearing capacity of the girder. The test results stated that the structural damage affected the bearing performance of this box girder. The deflection of the test girder in the uncracked stage did not meet the proof stiffness requirements under the variable load of highway bridge. The calculated results of the flexural bearing capacity are basically identified with the result from full scale flexural test, which is 70% higher than the design bending moment by the internal force of the main girder. The results of full-scale shear tests are respectively 32% and 37% higher than the internal shear design values of the girder. The formulas with damage reduction coefficient for calculating the bending and shearing capacity of the concrete box girders is applicable to evaluate the bearing capacity of the dilapidated concrete girders with more accurate results, which can provide a reference for the evaluation and maintenance of massive existing small concrete box girders in China.

Residual capacity of a reinforced concrete grillage deck exposed to corrosion

Grillage decks made of reinforced concrete (RC) with more than 40–60 years of service life may exhibit localised areas of severe damage or even entire elements exceeding the serviceability limits. In these cases, it is essential to quickly and efficiently assess the structure’s safety margins, and, in the worst cases, to also verify whether the damaged deck’s residual bearing capacity is sufficient for it to be used as a platform for the repair works. This article proposes an assessment based on a non-linear RC finite element specialised in dealing with systems working in bending and torsion. The damage, measured at a particular time after construction, is modelled by a reduction of the reinforcement section, supposed to be induced by chlorides diffusion and investigated through a Cellular Automata algorithm. Such an approach is applied in studying a bridge deck, having an edge beam damaged by leakage of salted water from the road platform. The results give a thorough description of the structural behaviour and the deformed shapes help in understanding the redistribution process of the internal forces. These results may provide a reliable reference to plan proper maintenance actions as well as to establish a hierarchy of repairing and strengthening interventions.

Mechanical behavior of cross-shaped steel reinforced concrete columns after exposure to high temperatures

Steel reinforced concrete (SRC) columns in a special shape are widely used in high-rise buildings. Due to their higher ratio of embedded steel members and larger fire exposure area compared to SRC rectangular or circular columns, SRC special-shaped columns always experience severer damage in fire. This paper experimentally and analytically investigated the residual strength of SRC cross-shaped columns after exposure to high temperatures. Experiments were conducted on eight column specimens which were heated first and loaded to failure after cooling down to room temperature. The influencing factors include heating duration, loading eccentricity and loading angle. The experimental results showed that all specimens subjected to shear failure, and their bearing capacity decreased significantly after high temperatures. With the increase of heating duration from 60min to 180min, the bearing capacity decreased by 20–27%. The bearing capacity decreased by 12–22% and 4–12% with the increase of eccentricities and loading angles, respectively. A simplified calculation method was proposed to determine the residual bearing capacity of SRC cross-shaped columns after exposure to fire. Its accuracy was validated against experimental results, which provided a reference for the post-fire assessment of SRC columns.

Bearing Capacity of Common and Damaged CFRP-Strengthened R. C. Beams Subject to High-Level Low-Cycle Loading

In the course of operation or armed hostilities the span r.c. structures are subject to substantial damage and considerable reduction of their bearing capacity, especially under low-cycle repeated loading. In this connection it becomes necessary to renew their operation capacity and/or improve their bearing capacity. However, the current design standards contain no recommendations as to determination of the residual bearing capacity of such structures and calculation of their reinforcement. There are methods of the operation capacity renewal and reinforcement of the structures by increasing their sections adding metal or reinforced concrete elements. Still, the calculation methods of such reinforcement are also imperfect. It is proposed to renew operation capacity of such structures by strengthening their tensioned parts with CFRP; the performed experimental research will provide the basis for calculating bearing capacity of said structures with the aid of the deformation method improved by the authors.

Failure tests and bearing performance of prototype segmental linings of shield tunnel under high water pressure

The occurrence and characteristics of structural failure under high water pressure and the evaluation of structural bearing capacity are of great significance in the rational design of shield tunnels. In this study, the failure process of two types of segmental lining structures used in the Shiziyang Tunnel in China, namely, the straight joint assembly structure (STRS) and staggered joint assembly structure (STGS), are investigated and summarized with prototype tests. The differences in the failure characteristics between the two types of lining structures are observed and analyzed, and two indexes are proposed to evaluate the damage status of the entire structure and local structure by analyzing and interpreting the failure phenomena during the tests. The results show that (1) The failure processes of both STRS and STGS under high water pressure perform as: the accumulation of previous occurred strength damage of segments ultimately leads to the displacement instability failure of structure. However, the difference is that besides the occurrence of large number longitudinal penetrating cracks at segments, there are local crushing and shear cracks occurred at the joints in STRS. (2) The failure processes of STRS and STGS under high water pressure can be divided into three stages: normal deformation stage, strength damage stage, and displacement instability stage. (3) With the proposed two indexes, the failure phenomena and structural bearing capacities at various stages of the failure process can be theoretically analyzed and quantitatively evaluated. The effective stiffness coefficient βe (specifically, βte for STRS and βce for STGS) is recommended to assess the structural bearing status, and the residual bearing capacity coefficient Rbc is suggested to evaluate the residual structural bearing capacity. (4) For STRS, when obvious cracks appear, βte is 0.83 and Rbc is 0.71; when significant deformation occurs, βte is 0.65 and Rbc is 0.52; and when the structure fails, βte is 0.4 and Rbc is 0.35. For STGS, when microcracks appear, βce is 0.67 and Rbc is 0.58; when the structure is significantly deformed, βce is 0.49 and Rbc is 0.43; and when the structure fails, βce is 0.18 and Rbc is 0.27. (5) In the loading process, βe and Rbc of STRS and STGS decrease constantly. For STRS, the two indexes rapidly decline after visible cracks appear, but for STGS, the decreasing amplitude is relatively small.

To determination of dependence of parameters of surface cracks in concrete and reinforced concrete volume elements

To determine the dependences of the parameters of surface non-through cracks, the problem of tensile bulk concrete elements (in the form of prisms) was considered. One group of elements contained a crack normal to tensile forces, and the other was inclined (the problem was modeled using the finite element method in the Ansys software package). The stress intensity factors of three types were determined, for which a macro (subroutine) was written in the APDL language, the calculated coefficients of the 2nd and 3rd type (KI, KII) were used for the first time in the considered problems. On the basis of these coefficients, relations between the length, width of the opening, the penetration of cracks are established, the boundaries of the pre-fracture zone are found, and the residual bearing capacity of the elements with a crack is estimated. It is shown that the stress relief area around the crack has a diamond shape. The dependences obtained and the procedure for obtaining the numerical values of KI abd KII constitute a scientific novelty.

Normative Service Life Of Concrete And Reinforced Concrete Structures And Principles Of Their Design Based On Durability Parameters

The paper systematizes the main criteria necessary to determine the standard service life of concrete and reinforced concrete structures; the state of domestic and foreign regulatory framework is analyzed in terms of requirements for the service life of reinforced concrete structures; the main normative and technical documents are considered in the field of life cycle design of reinforced concrete structures of buildings and constructions. The types of corrosion damages of reinforced concrete structures and their determining factors are described; the internationally agreed models of durability for some degradation processes are given. On the basis of the work carried out, proposals were prepared to assess the corrosion state of the exploited reinforced concrete structures, their residual bearing capacity, operational serviceability, expected service life under specified aggressive actions, and methods for determining the standard service life of reinforced concrete structures. Proposals for the development and updating of a number of relevant regulatory, technical, organizational and methodological documents are given.

Possibilities of evaluation of the masonry wall affected by the explosion

At present, emphasis is placed on the safety and durability of building structures due to the effects of external loads. Among the various external influences of the load, we can also include loads caused by the blast wave. Structures subjected to extreme loads such as explosion are structurally disrupted in a manner different from that of static or dynamic external loads. In construction practice, we are sometimes faced with the question of how to evaluate the state of a structure after an explosion. The article is focused on the possibility of evaluating the masonry wall affected by the explosion in terms of the expression of residual bearing capacity based on the laboratory tests and inspection in-situ.

Residual bearing capacity of infilled frame of multi-ribbed composite wall after high temperature

Multi-ribbed composite wall structure (MRCS) is composed of densely distributed ribbed frames, including ribbed beams and columns and autoclaved aerated concrete (AAC) filled inside ribbed frames. This paper investigates the temperature field and residual capacity of the infilled frame of MRCS after high temperature based on a combined experimental and finite element (FE) study. A series of axial compression tests were conducted to evaluate mechanical properties of AAC, including compressive strength, elastic modulus and peak strain, subjected to high temperature. The constitutive relation of AAC after high temperature is defined based on stress-strain curves under different temperatures. Temperature field of the infilled frame under different fire loading schemes and the temperature of each node at different heating time are obtained from numerical analysis on basis of the thermodynamic performance of each material. Based on this, a Finite Element (FE) model for the infilled frame under diagonal loading is constructed, and the relationship between the residual bearing capacity and fire exposure time under different fire conditions is obtained.

An Assessment Method for Residual Bearing Capacity of RC Bridges After Fatigue Damage

In order to realize the in-situ evaluation of reinforced concrete bridges subjected to fatigue for a long time, an evaluation method for cumulative damage of concrete structures based on unloading elastic modulus is proposed. First, according to the concrete stress-strain curve and the statistical relationship between residual strain and cumulative strain, the calculation method of static equivalent strain and residual strain concrete based on unloading elastic modulus and the method for estimating the strength of concrete after damage are proposed. The detailed steps of field test and analysis and the practical damage indicators of residual strain are given. Then, the evaluation method of existing stress and strain of Reinforced Concrete Bridge under dead load and the concept of “equivalent dead load bending moment” are put forward. On this basis, the paper analyzes the root cause of the decrease of bearing capacity of Reinforced Concrete Bridge after fatigue damage, and points out that the equivalent strain or residual strain of reinforced concrete increases under the fatigue effect, which leads to the decreasing of actual live moment and deformation performance while the ultimate load-carrying capacity remains constant or very little decrease. The evaluation method of structure residual capacity is given, which has reference value for engineering practice.

Low-cycle fatigue behavior of glass-fiber-reinforced polymers cross arms with steel sleeves

For the dynamic fatigue problem of transmission tower cross arms caused by the strong wind load, an experimental study on low-cycle fatigue behavior of a new type full-scale glass-fiber-reinforced polymers (GFRP) cross arm with steel sleeves was carried out. A total of six specimens were subjected to cyclic loading for simulating low-cycle fatigue. The stress state was monitored. The variety of load-displacement-time curve, energy dissipation and dynamic strain were analyzed. The ultimate bearing capacity of the specimens without significant fatigue failure was examined to derive residual bearing capacity. Based on the residual strength theory, the cumulative damage was evaluated to predict the fatigue life. It is shown that the GFRP cross arms demonstrated favourable anti-fatigue performance, and can be expected to provide important reference for wind res istance design in transmission tower line system.

Influence analysis of the main types of defects and damages on bearing capacity in reinforced concrete elements and their research methods

Abstract In current economic trends, changes in construction using are required. It usually leads to changes in value and type of the working load on building structures, with the requirement to rate the technical state and replace or strengthen the elements. An important aspect of determining the residual bearing capacity of damaged bending reinforced concrete elements is the research concerning the influence of difference defects and damages on the change of strength and deformability. In the article main types of damages and defects, methods of studies of damaged reinforced concrete elements and the expediency of usage of this elements are described. However, most methods are suitable only for certain defects and damages due to the large complexity of calculations and the consideration of multifactoriality. Significant complexity of a single method for calculating damaged elements depends on the possible changing stress strain state of an element in combination with certain defects and damages, the presence of a non-complete separation where during loading or alteration of the damaged element the fractions become included in the work, reinforced concrete is the composite material which carrying complexity in calculating the joint work of its components.

Residual bearing capacity of reinforced concrete columns after close-in detonations: experimental and numerical investigations.

Residual bearing capacity of reinforced concrete columns after close-in detonations: experimental and numerical investigations.

The effect of cracks on the bearing capacity of reinforced concrete slabs

Cracks occur in reinforced concrete slabs for two reasons - due to increased operational loads and due to manufacturing and installation defects. When cracks are detected, the question arises about the residual bearing capacity of the slab and the need of its strengthening. To solve this problem by calculation, it is necessary to take into account physical nonlinearity. An algorithm for the calculation by the finite element method is proposed. The main feature of the algorithm is the use of multilayered finite elements, which allows modeling the cracks by specifying the corresponding material characteristics of those layers which the crack passes through. A method for determining the bearing capacity of a slab with cracks after its reinforcement with composite fabrics is also considered. An example of the study of the stress-strain state of a reinforced concrete slab with cracks by the proposed method is given. The implementation of the algorithm in the PRINS program is described and the possibility of using this program for solving practical problems is discussed.

Damage Model Test of Prestressed T-Beam Under Explosion Load

Bridge is an important infrastructure in road traffic, which may bear the accidental load of terrorist attacks and transportation accidents and explosions in its life cycle. In this paper, three groups of prestressed T-beam model tests were carried out in response to the terrorist explosion on the bridge deck. The results show that with the increase of explosive equivalent, the failure degree of prestressed steel reinforcement is aggravated, the number of anchorage falling off is increased, and the normal steel reinforcement evolved from failure to fracture. The fracture shape of the web of prestressed T-beam was “X”, and the failure form on both sides of the web was roughly “I” shape. The number of concrete cracks increased, and the crack depth and the size of the crack increased. The local failure mode of T-beam evolved from seismic collapse to penetrating failure, and the residual bearing capacity of prestressed T-beam gradually decreased.

UNDERGROUND DEVELOPMENT OF ORE DEPOSITS WITH CONSERVATION OF THE GROUND SURFACE

Introduction. In a market economy of particular importance are indicators of the quality of raw materials. Loss and decontamination of ores can be achieved by controlling stresses and strains using the residual bearing capacity of the fractured rocks with the primary condition of preserving the earth's surface of destruction. Goals and objectives. The purpose of the study is to substantiate the rational parameters of the technology of the geodynamic safety criterion. The goal is achieved by solving a complex of production due to technical problems, ensuring the correctness of the results, the assessment of geomechanical condition before the development of preventive measures of the impact of mining operations on the environment. Methods. Research methods include system and analysis of theory and practice results, experimental research and scientific forecasting. Results. The value of the criterion of optimum processing technology in the form of preservation of the earth's surface of destruction, such as guarantees of contact of the zone of destruction of the massif of mining, the zone of living matter, flora, fauna and Humans. A detailed understanding of the mechanism of interaction of the structural blocks of a discrete gravitational-tectonic-structural field. The mechanism of manifestation of the residual bearing capacity of the destroyed structural rock separations, the limitation of the degree value, the optimization of the mixture strength and the size of the pillars, the creation of geomechanical balanced segments with the minimization of the costs of the earth's surface condition control are specified. The proposed classification of methods of calculation of extent of the flat roof. The given classification of the methods of array management differs from the assessment of the state of the developed space during the work, after the end of the redemption, and not during the cleaning dredging. An example of the earth's surface conservation is given for the development of a flat-falling field, preserving the earth's surface without filling voids. Conclusion. The processes of control of the state of the masses and the earth's surface are their equivalent, which allows monitoring of the development of the field at all stages of the enterprise's existence. The use of geomechanical factors for the organization of mineral raw materials, mining tool for the implementation of resource-saving and environmental protection trends of mining production and reserve to improve the quality of the extracted ores when to ensure the competitiveness of the enterprise.

Comparison of Static and Fatigue Behaviors between Stud and Perfobond Shear Connectors

This paper presents an experimental evaluation for comparison of the behaviors of stud and Perfobond shear connectors under static and fatigue loading based on 20 push-out tests. The push-out tests for each type of shear connectors including three series: static tests, fatigue endurance tests and residual mechanical properties test, respectively. In static tests, the failure modes of two types of connectors are different. The elastic stiffness and ultimate slip in the load-slip curves of the Perfobond are larger than that of stud. In fatigue endurance tests, the fatigue life of the studs is 2.68 million, while the Perfobond specimens do not fail after 3.0 million numbers of cycles under the same test conditions as studs’. Compared with the stud, the relative-slip of Perfobond increased sharply in the early period. In residual mechanical properties tests, the residual bearing capacity, shear stiffness and ductility are presented and discussed. The variation rules of these three indexes for two types of connectors are the same, while the indexes of Perfobond are much larger than stud’s throughout the process. The results indicate that Perfobond connector has good ductility, better fatigue resistance and higher safety reliability. However, the economy of Perfobond connectors is not as good as studs’.

Failure characteristics of large unconfined cemented gangue backfill structure in partial backfill mining

For the subsidence prevention purpose, partial backfill mining is employed. The mined-out area is supported by carefully designed backfill piers and strips. The stability of these unconfined backfill structures (UBS) is very important to the mining operation. In order to study the failure characteristics of UBS, the stress-strain curve of a large cemented gangue backfill material (CGBM) test block (800 × 800 × 800 mm) was derived through uniaxial compression test. The failure process of the test block was monitored by digital image correlation (DIC) and ultrasonic testing (UT) techniques. The internal pressures and deformations were monitored by sensors embedded at different depths in the test block. It is found that: 1) The curves of internal pressure and deformation can be divided into four stages. 2) A hard core is formed in the central part of the test block under uniaxial compression load. 3) The three manifestations of the curves of internal pressure or deformation can be used as the failure precursor point, critical instability point, residual bearing capacity or residual deformation of the test block respectively. The experimental findings could be used to guide the design, stability monitoring and reinforcement of UBS in partial backfill operations.

Applicability Analysis of Assessment Methods for Morphological Parameters of Corroded Steel Bars.

The irregular and uneven residual sections along the length of a corroded steel bar substantially change its mechanical properties and significantly dominate the safety and performance of an existing concrete structure. As a result, it is important to measure the geometry and amount of corrosion of a steel bar in a structure properly to assess the residual bearing capacity and service life of the structure. This paper introduces and compares five different methods for measuring the geometry and amount of corrosion of a steel bar. A single 500 mm long and 14 mm diameter steel bar is the specimen that is subjected to accelerated corrosion in this protocol. Its morphology and the amount of corrosion were carefully measured before and after using mass loss measurements, a Vernier caliper, drainage measurements, 3D scanning, and X-ray micro-computed tomography (XCT). The applicability and suitability of these different methods were then evaluated. The results show that the Vernier caliper is the best choice for measuring the morphology of a non-corroded bar, while 3D scanning is the most suitable for quantifying the morphology of a corroded bar.

Combined Way of Diagnostics of Reinforced Concrete Conical Structures

Reinforced concrete conical structures are the basis of safety and operational reliability of railways power supply systems. The article presents optimal methods for diagnostics of reinforced concrete structures, which allow recommending the sequence and amount of repair work aimed at restoring or maintaining the required state of reinforced concrete conical section structures (contact-line supports, power transmission line supports, etc.). A design scheme is proposed for determining the residual bearing capacity of the support in the presence of cracks and corrosion of the reinforcement.