Takumi Shimomura

Systematic Laboratory Test on Structural Performance of Corroded Reinforced Concrete and Its Utilization in Practice

A great number of loading tests have been performed on load-carrying behaviour of RC members with the corroded reinforcing steel. However, it is difficult to find the quantitative relationship between the degree of corrosion and the loading capacity. This may be attributed to a scatter in the results of the loading test due to the non-uniformity in the reduced cross sectional area of the corroded reinforcement and some differences in the experimental technique. Such scatter of the results also leads to the difficulty in the selection of the target of the numerical analysis, which must be useful for the estimation of the structural performance. JSCE (Japan Society of Civil Engineers) Committee 331 conducted a systematic laboratory test on the structural performance of RC beam deteriorated by the corrosion of the reinforcement according to the common experimental procedure. The objectives of the common test are to grasp the essence of the scatter in the result of load-carrying capacity. In this study, the flexural behaviour of RC beam, which is degraded due to the chloride ion attack, was focused on without taking into consideration shear failure or bond failure of the tensile reinforcement. The results of the common test show that the large ratio of the corrosion weight loss was highly likely to induce the failure due to the fracture of the longitudinal reinforcement, because the longitudinal scatter in the cross-sectional area of corroded reinforcement increases as the corrosion loss increases.

Modelling and Nonlinear FE Analysis of Deteriorated Existing Concrete Structures Based on Inspection

In evaluating structural behaviour of deteriorated existing concrete structures by numerical analysis, it is important to properly detect and quantify material deterioration in the objective structure by means of conducted on-site inspection and to adequately consider them in terms of FE modelling. When the deterioration level of the structure is low, its structural behaviour can be estimated by a common numerical method with sound structure as much as the effect of deterioration is considered in constitutive models. In case of heavily deteriorated structure, however, the way of macroscopic modelling of deteriorated portion has great influence on analytical results. In addition, since an actual structure is generally composed of number of structural members having various levels of deterioration, it is essential to analyze whole the structure instead of part of the structure in order to know overall performance of the structure adequately. In this paper, a general procedure for nonlinear FE analysis of a deteriorated existing concrete structure based on on-site inspection is proposed and an integrated case study of analysis of a concrete bridge with reinforcement corrosion is demonstrated.

Simulation of Time-dependent Tensile Behavior of Concrete under Various Loading and Drying Path

Stress analysis, considering spatial distribution of shrinkage and time-dependent deformation characteristic, should be carried out in order to predict accurately tensile stress and associated crack in concrete member under restraint drying shrinkage. In particular, a constitutive model for concrete that can adequately express tensile creep under drying is of importance. A new apparatus for sustaining tensile test of concrete was developed in this study to obtain reliable data of tensile creep of concrete, which can be a basis to develop an accurate computational model. The testing system, using cylindrical specimen, ensures comparison between experimental and analytical results under ideal conditions. Tensile stress and strain of the specimen can be precisely and stably controlled by inducing tensile load into the specimen as a reaction of compressive load in steel rod connected by screw. Consequently, time-dependent tensile behavior (i.e., stress, strain and cracking) of concrete can be tested under various loading and drying path programs. Test results obtained the proposed apparatus are demonstrated. Numerical simulation of tensile behavior of concrete is also conducted in this study. It was verified that reduction of tensile stiffness and cracking stress of concrete under drying can be simulated by strain softening near the surface due to restrained shrinkage.

Loading Test of RC Beam Bridge Built 80 Years Ago in Japanese Coastal Area

Many concrete structures have to be now repaired or replaced due to salt attack in Japanese coastal area. However, their residual strength is not well considered in practice. This is because only few studies have so far been made on the residual strength of deteriorated concrete structures. Objective of this research is to study about the load carrying capacity and the failure behaviour of corroded real RC bridge. Firstly, we sawed the reinforced concrete bridge to take out beam specimens. The bridge was seriously corroded because it was built about 80 years ago in Japanese coastal area. Two beam specimens were carried into experimental room and loaded until failure. Load carrying capacities of these two specimens were quite different. Maximum load of the relatively sound beam was about 96% of the estimated capacity of non damaged beam. On the other hand, the relatively deteriorated beam had only 48% of load carrying capacity. To examine the cause of the reduction in loading strength, layout of reinforcement and corrosion rate of longitudinal bars in concrete were carefully inspected. In the inspection, several lap splices were found in tensile area while the difference in corrosion rate is much smaller than the difference in strength. Thus, the cause of reduction in loading capacity is considered as bonding failure at lap splice. Finite Element analysis was conducted to simulate test results. It was confirmed that FE analysis can estimate the structural behaviour of test beams if the bond strength of each lap splice is obtained first.

NUMERICAL SIMULATION OF LONG-TERM BEHAVIOUR OF CONCRETE STRUCTURES WITH EXTERNALLY BONDED CONTINUOUS FIBRE SHEET

ABSTRACT A numerical simulation of long-term behaviour of concrete structures retrofitted with externally-bonded continuous fibre sheet is presented. Continuous fibre sheet can improve not only mechanical performance of an existing concrete structure but also its durability. The effectiveness of continuous fibre sheet as a surface insulator was quantified by laboratory tests. Based on this, case studies of numerical service-life simulation of concrete structures with continuous fibre sheet under corrosive environment are demonstrated. The results imply that continuous fibre sheet can extend service-life of concrete structures.

Evaluation of critical crack width for reinforcement corrosion in RC member based on numerical simulation of transport of chloride ions in concrete

Chloride-induced reinforcement corrosion in reinforced concrete structures exposed to marine environment is one of the most important factors affecting the durability of structures. To minimize the effect of cracks on the deterioration of RC structures, current design codes often limit the crack width. However, recent investigations indicated that condition of steel-concrete interface is a more essential criterion related to reinforcement corrosion. The purpose of this study is to clarify the effect of various conditions including cover thickness, water-cement ratio, environment action and interfacial void on limitation of crack width. The validity of crack width limitation in design codes is discussed based on analytical results.

Probabilistic Approach to Service Life Prediction of Concrete Structures Subjected to Load and Environmental Actions

In the design of reinforced concrete (RC) structures in a marine environment, it is important to consider the effects of this environment on structural long-term performance. In this paper, a time-dependent structural reliability analysis method taking the hazard associated with airborne chlorides into consideration is proposed. Also, a procedure to obtain the failure probabilities of RC structures in a marine environment updated by Sequential Monte Carlo Simulation (SMCS) is indicated. In this procedure, the corrosion crack width is used as observational data. For illustrative purposes, time-dependent reliability analyses are presented for one-way RC slabs in a marine environment. Using SMCS, multiple random variables related to observation information can be updated simultaneously. This is realized by taking into consideration the joint probability density functions of the random variables. The effects of the hazard associated with airborne chlorides and an inspection result of corrosion cracking on the updated estimate of one-way RC slab reliability are discussed in this study.