Baidar Bakht

SOIL-STEEL BRIDGES

A soil-steel bridge is a structure made with a shell of manufactured curved corrugated steel plates and an envelope of engineered soil, which is well-compacted backfill composed mainly of well-graded granular soil. A photograph of a soil-steel bridge serving as a grade-separation structure is presented in Fig. 7.1. These structures are, however, also used to convey water, in which case they are appropriately referred to as culverts. A soil-steel bridge with a twin conduit serving as a culvert is shown in Fig. 7.2.

Arching in Deck Slabs

The term deck slab is typically used in North America to describe the concrete slab of a girder bridge which supports the vehicle loads directly before transmitting their effects to the girders. In this chapter and elsewhere in this book, the term is used with this same meaning, rather than to describe a slab bridge as is done in some countries.

Rehabilitation with FRPs

The acceptance that fibre reinforced polymers (FRPs) have so far gained for new structures is not in proportion to their potential, because their short-term costs are usually higher than those for structures with conventional materials. Designers and owners have usually justified the use of FRPs in new structures on the basis of life-cycle costing. The same is not the case for rehabilitation of existing structures with FRPs. The FRPs are highly cost-effective for rehabilitation, mainly because of their light weight and ease of bonding them to existing structures. A few of the several innovative applications of FRPs in this respect are described briefly in the following Sections, it being noted that the design provisions of all these rehabilitation techniques are covered by the Canadian Highway Bridge Design Code (CHBDC 2006). It is recalled that the CHBDC defines rehabilitation as ‘modification, alteration, or improvement of the condition of a structure that is designed to correct deficiencies in order to achieve a particular design life and live load level.

Structural Health Monitoring

Structural health monitoring (SHM) is the integration of a sensory system, a data acquisition system, a data processing and archiving system, a communication system, a damage detection system and a modeling system to acquire knowledge about the integrity and load-worthiness of in-service structures on either a temporary or continuous basis.

Analysis by Manual Calculations

In structural engineering, the term usually refers to in which the distribution of force effects is determined in the various components of a structure. The responses of a structure such as deflections and bending moments are often referred to as load effects. Another infrequently used term in structural engineering is which refers to the process of determining the strength of the whole structure or its components. The term is used in this book only in the meaning of force analysis.

Bridge Weighing-in-Motion

In a realistic bridge design code, the design live loads should be based on actual traffic loads, as discussed in Chap. 1. In the past, the information about the actual traffic loads on highway bridges was obtained from truck surveys, in which the trucks are stopped for measurement and weighing on ‘static’ weighing scales. During the past few decades, however, the information about the truck loads is collected while the trucks are moving at normal speeds. Some of the weighing-in-motion (WIM) scales are installed in the pavement. In other WIM systems, a highway bridge is used for the weighing-in-motion of the trucks; this latter system is referred to herein as the bridge WIM (BWIM) system, and the system installed in the pavement as simply the WIM system. The WIM systems are significantly more expensive and are expected to be more accurate than the BWIM systems.

Fibre Reinforced Bridges

In 1989, the authors of this book and their friend L.G. Jaeger (1926–2013) wrote a brief article inquiring if the time had come in Canada for the use of the advanced composite materials, now known as fibre reinforced polymers (FRPs), in civil structures (Mufti et al. 1989). The premise for the apparently affirmative answer to their query lay in the promise of the high durability of FRPs in concrete in corrosive environments, in which steel-reinforced concrete deteriorates rapidly and is thus not sustainable. Since the late 1980s, the considerable research into the use of FRPs in civil structures has led to centres of excellence, and several series of international conferences with voluminous proceedings recording a very large body of research into the subject.

Analysis by Computer

As discussed in the introduction to Chap. 2, the term is being used in this book for the determination of load effects in the various components of a bridge superstructure subjected to vehicle loads. The methods employed for bridge analysis range in complexity from the overly simplified D-type method of AASHTO (1989) to highly complex finite element methods. The earlier AASHTO simplified method of analysis, because of being too simple, is often excessively conservative. The finite element methods, which require fairly complex computer programs, on the other hand are prone to common errors of idealization and interpretation of results; the former difficulty is discussed with the help of specific examples by Mufti et al. (1994). The large quantity of numerical output associated with finite element analyses also tends to deprive the designer of the physical feel of the behaviour of the structure.

Loads and Codes

Although not generally appreciated by lay people, it is not possible to design and construct a structure that will remain safe against failure under all conditions and at all times.