Precast prestressed girder bridges can be made continuous for live load if the deck and diaphragm are cast with sufficient positive and negative moment reinforcements. The continuity eliminates costly joints and enhances seismic performance, structural integrity and overall durability of the structure. If diaphragm is poured with sufficient negative moment reinforcement before the deck is cast, continuity may also apply to the dead load of the slab. Although, connection of the girders at the diaphragm varies from state to state, it generally consists of bent bars or bent strands. Also, a short length of the girder may be embedded into the diaphragm. The continuity connection is a doubly reinforced section, which requires a time-dependent analysis including differential shrinkage, creep due to prestressing and dead loads, and temperature effects. These time-dependent effects can result in considerable positive restraining moments at the supports, which can in turn crack the diaphragm or pull the girder out of the diaphragm. These positive moment cracks are not only unsightly, but may also result in durability issues for the bridge. Furthermore, it questions the integrity of the continuity connection. The paper examines the extent of positive moment cracking based on field observations, time-dependent analysis, and previous studies.

This paper provides an outline of the provisions for design for cracking given in the current version of Eurocode 2; the Eurocode for the design of concrete structures. The basic theory underlying the clauses is derived, the content of the clauses themselves are outlined and the development of simplified detailing rules for the control of cracking is considered.

A reconnaissance visit was conducted to Turkey shortly after the August 17, 1999 Earthquake to investigate the performance of concrete structures. The dominant form of construction in the area was reinforced concrete frames, infilled with masonry walls. Extensive cracking and damage was observed in most structures located in the disaster area. This paper presents an overview of the types of cracking that can be expected after a seismic activity, as well as those observed after the August 17, 1999 Earthquake in Turkey. Causes of seismic damage are discussed with examples. A brief review of the seismological aspects of the earthquake and the overall performance of reinforced concrete buildings are provided.

Shrinkage reducing admixtures (SRA’s) are a new type of admixtures which is effective in reducing the drying shrinkage of concrete. SRA performance has typically been evaluated on the basis of unrestrained drying shrinkage tests. However, it is usually the cracking performance of concrete when shrinkage is restrained that is of primary interest to the marketplace. The current paper presents an evaluation of SRA’s based on several parameters: free shrinkage, tensile stresses which develop in a uniaxially restrained rig, and the sensitivity to cracking in such conditions. The positive influence of SRA’s on all of these three parameters is demonstrated. A comparison is made between the effect of SRA and of low-volume, polypropylene fiber reinforcement. The latter is known to be effective in controlling early age plastic shrinkage cracking. The present data show that in the case of hardened concrete, after one day of curing, low volumes of fibers do not give any advantage, and it is in this range where the SRA is effective. Thus, the two types of additives can complement each other: the fibers are efficient in controlling plastic shrinkage cracking while the SRA can take over the role of crack control in the hardened concrete, where low volume-low modulus fibers are not effective.

AC1 3 18-99 no longer refers to Z factors or crack width formulae as in previous editions of the code. Instead, AC1 318-99 correlates bar spacing with clear concrete cover, indicating that following these guidelines will reduce crack widths at the concrete surface. Field investigations have found leakage at certain type cracks which exhibit widths of .23mm (0.009”) or greater. Research and condition surveys completed by the author have found greater potential for concrete deterioration at cracks which extend to embedded reinforcement as compared with low slump, low water/cement ratio concrete having adequate cover over reinforcement. Current codes and standards present considerable variation with regard to recommended maximum crack widths to prevent leakage. Use of AC1 3 18-99 to design liquid or gas retaining structures could lead to designs that are not conservative, not durable and possibly unsafe, if preventing leakage is an important requirement for the particular facility.