International Concrete Abstracts Portal

An analytical procedure is described for predicting the development of vertical cracks in thin-walled and thick-walled cylindrical structures subjected to membrane forces and thermal loads. Sustained, axisymmetrical (thermal) loads and thermal cyclic loading may jeopardize, due to cracking, the serviceability (in this case the tightness) of thin-walled cylinders. Mathematically obtained crack patterns have been compared with field observations: a good agreement between theory and practice could be established from this comparison. On the basis of a reliable prediction of crack patterns, cost-benefit analyses are feasible to weigh crack control measures against possible repair costs in case these measures were neglected. An example of such an analysis shows an initial increase of reinforcement in view of crack control to be preferable to repair (grouting) of cracks.

Concrete bridge decks have long been a problem for the design and construction industry. They have a tendency to crack and/or spall over time. The deicing process then creates problems because of salt intrusion into cracks. These cause spalling and ultimate deterioration of the reinforcing steel and the load-carrying ability of the concrete slab. The author wrote specifications concerning methods to produce a bridge deck that should be relatively crack free and thus enhance the long-term durability of the slab. Some items specified included long-term wet-mat curing, better concrete quality control, and a reduction of the water-cement ratio by 20 percent below standard specifications. He further discusses the utilization of retarders and high-range water reducers to accomplish the objective. The author then covers other methods in the literature such as epoxy-coated reinforcing bars as part of the overall process to produce a bridge deck that is relatively maintenance free over the long term.

Presents a simple design aid for predicting long-term (up to 50 years) movements in reinforced concrete columns and bridge beams made of normal and lightweight aggregate concrete. The method is based on the principle of superposition using a creep factor chart, which takes into account varying sizes of members, age at loading, exposure conditions, and the percentage of reinforcement, and it requires only a knowledge of the concrete strength and the loading history of the member. The method is developed from the study of in situ movements in two reinforced concrete structures subjected to increment loading. The shrinkage strains in columns are predicted using a shrinkage chart, which requires only a knowledge of elastic modulus of concrete at 28 days. The predicted load-induced and basic strains show excellent agreement with measured strains in the two structures, and the method shows good agreement with literature. The paper demonstrates how the simple method of predicting long-term movements in buildings and bridges can be utilized by the structural engineer as a designer's tool.

In seismic zones, severe earthquakes occur within a certain period. However, the important functions of a concrete structure must be maintained after the earthquake. Hence, structures must be designed for safety during the earthquake and serviceability after the earthquake. The acceptable level of damage can be varied in accordance with the type and importance of the structure. When a reinforced concrete structure suffers significant plastic deformation, residual deformation and large crack opening in the structure are impaired. A new and rational seismic design method was proposed. The peculiarity of the concept of the design method is as follows: Seismic design should be performed to fulfill required serviceability after the design earthquake as well as required safety during the earthquake. High magnification factor due to dynamic response was introduced according to actual observation in the earthquakes. Reduction factor referred to the acceptable level of damages in the structure after the earthquake was introduced. The importance of design details was emphasized. Furthermore, the influence of axial compressive force on the ductility was pointed out.

A rational method of analysis is developed that can be used on a computer to determine the behavior of reinforced concrete columns under sustained service loads. At specific time intervals, trial-and-error procedures are used to establish strain compatibility and equilibrium conditions at each of several cross sections of a member. Curvatures are integrated to find the deflected shape, and an iterative approach is used to find the stable deflected shape if there are secondary moments. The analysis calculates the effect of creep on the stress redistribution between concrete and steel and on the deflections of members subjected to variable axial loads and variable moments. The effects of shrinkage and cracking are also included. The applicability of the analysis is partially verified by comparison with laboratory and field investigations reported by various researchers. In most cases, a good correlation is obtained between the analytical results and the measured results.