Single vehicle method

This procedure gives a more precise assessment than the method described previously. It may be used where the standard design life of 120 years or the annual flow given in Table 6 are not applicable. However, the procedure may only be used if the detail under assessment can be classified using Table 17 of the Code, but is not a Class S detail and the fatigue loading is the standard load spectrum. Figure 84 outlines the basic steps in this method of assessment. Figure 9 of the Code used in this...

Introduction

An efficient transportation system plays a vital role in the development of a modern society, mainly due to the inter-reliance of various industries and the increased trend for outsourcing of various necessary ingredients within a single activity. Hence, transportation networks are referred to as lifelines, the integrity of which has to be protected alongside water supply, electricity and gas networks. While roads are a most important component of transportation networks, bridges are both more...

Vehicle impact

It is not usually necessary to undertake dynamic analysis of vehicle impacts on bridges as most international bridge codes prescribe quasi-static collision forces based on full-scale testing. In the UK, Highways Standard BD 60 94 (Department of Transport, 1994) provides guidance on the application of equivalent static impact forces to bridge substructures and superstructures. Where retrofitting of older bridges is required to provide enhanced collision protection, the adoption of dynamic impact...

Remarks

It is indeed noticeable that more recent earthquakes cause more damage to structures, notwithstanding the advancement in seismic design practice. This is due to the increased number of bridges of complex configurations coupled with the heightened consequences of bridge damage in developed societies. The above quick overview of damage patterns sets the scene for considerations of layout and configuration that go a long way towards ensuring the seismic safety of bridge structures. If the general...

Materials Concrete

The required strength of the concrete is determined by the compressive stresses generated in the concrete by the pre-stress and applied forces. A minimum strength offu equal to 45 N mm is typical for prestressed concrete however, it is becoming more common to use higher strengths with fu up to 70 N mm2 not unusual, while even higher values have been achieved for some projects. The rate of gain of strength of the concrete is important as this governs the time at which the prestress can be...

Single mode analysis

Single DOF analysis is often termed equivalent static analysis in seismic design codes. It is the most basic form of analysis and is appropriate for bridge frames whose response is captured by a predominant translational mode of vibration. The predominant natural frequency of the SDOF system shown in Figure 27 is determined using the methods described in 'Principles of structural dynamics', above. In undertaking this calculation it is critical to ensure that account is made for all the relevant...

Performance based seismic design

A number of recent seismic codes including AASHTO-LRFD (2007) and Eurocode 8 (2004) have promoted the adoption of performance based seismic design for bridge structures. Performance-based design is based on ensuring that the displacement demand under the design seismic event does not exceed the structure's displacement capacity on the basis of the non-linear moment curvature capacity of the ductile elements of the structure, principally the columns. Given that the technique is mainly a design...

Strands and tendons

A seven-wire strand with a tensile strength of 1860 N mm2 and either 13 or 15 mm diameter is a very common form of prestressing and can be used either singularly for pre-tensioning or in bundles to form multi-strand tendons for post-tensioning as shown in Figure 2. The most common post-tensioned tendon sizes utilise 7, 12, 19 or 27 strands to suit the standard anchor blocks available, but tendons can incorporate up to 55 strands for larger tendons. Stressing to 75 ultimate tensile strength...

Comparison of provisions

A number of studies comparing seismic codes from the USA and other countries is available in the literature (e.g. Rojahn et al., 1997 Kawashima, 2000b Yen et al., 2003). A comparative study between the seismic design specifications for highway bridges of the US and Japan was reviewed and compared by Yen et al. (2003). In the comprehensive study of Rojahn et al. (1997), the USA codes, namely AASHTO, ATC and Caltrans, were compared. Also included in the latter study were the codes of New Zealand,...

M

Pitching coefficient, CM --m m (58) where D, L and M are the wind axis along- and across-wind force and pitching moment. Vm is the mean wind speed, is the density of air (in the UK taken as 1.225 kg m ) and B is the reference dimension which is usually the deck width. Force coefficients must be corrected to account for blockage effects due to the confining effects of the wind tunnel. A number of methods for calculating correction factors have been proposed and reference to specialist literature...

Info

Forces that are coupled to the motion of the structure. These instabilities are grouped into two broad categories. Divergent amplitude response includes phenomena such as galloping, stall flutter and classical flutter that result in rapidly increasing oscillations which must be avoided if structural failure is to be prevented. Galloping instabilities arise on certain types of bridge deck cross-section due to the variations of wind drag lift and pitching moments with wind incidence angle and...

Compaction pressures

The application of compaction plant, such as heavy vibrating rollers, to abutment backfill in layers leads to temporary but quite large increases in both vertical and horizontal stress within the fill. Some of these stresses remain locked Locus of maximum compaction pressure Figure 12 Compaction pressure - granular fill (Clayton et al., 1993) Locus of maximum compaction pressure Figure 12 Compaction pressure - granular fill (Clayton et al., 1993) into the fill, and can give considerable...

Time domain methods

Dynamic analysis undertaken in the time domain requires an incremental method in which the equilibrium Equation (1) at each point in the structure is solved at times At, 2At, 3 At, etc. There are a large number of incremental solution methods, many of which are implemented in modern structural analysis software. Linear elastic problems are most efficiently solved using Duhamel's method, described above, using a modal analysis technique. This approach is capable of providing very rapid solutions...

Computational fluid dynamics

Computational Fluid Dynamics (CFD) is a computer modelling technique for simulating fluid flow. CFD predicts air speed and direction, including the presence of vortex shedding. CFD is a tool that is gaining in popularity amongst bridge engineers and is useful for refining the shape of bridge decks prior to wind tunnel testing in order to eliminate features that instigate excessive vortex shedding. An example of a CFD analysis for the cable-stayed deck section of the Vasco da Gama Bridge in...

Snow and ice

In certain parts of the world snow and ice are in evidence for considerable periods and in the case of cable-stayed and suspension bridges can contribute significantly to the dead weight by forming around the cables, parapets and on the supporting towers. Complete icing of the parapets also means that lateral wind forces are increased due to the solid area exposed to the wind. Expansion joints and bearings can also become locked resulting in large restraining forces to the deck and...

Prestressing tendons

High-tensile steel is used as wire, strand or bars, with nominal tensile strengths varying between 1570 and 1860 N mm2 for wire or strand, and between 1000 and 1080 N mm2 for bars. After the load is applied to the prestressing steel, stress relaxation occurs which results in a reduction of the force in the tendon. The magnitude of relaxation varies depending on the steel characteristics and the initial stress levels applied, with typical values of 2.5-3.5 when a stress of 0.70fpu is applied,...

Vortex excitation

The critical wind speed for vortex excitation is based on the Strouhal number f frequency of vortex shedding d diameter of stay V wind speed. For a cylindrical cable, S is equal to 0.2 which gives the critical wind speed, Vc 5wd, where the natural frequency of the cable. The risk of significant vibrations occurring is a function of the Scruton number, Sc. When Sc is greater than 20, there is little risk of significant vibrations due to vortex excitation. mc mass per unit length (kg m) Ss...

Swelling pressures

Compaction of cohesive fill produces even greater increases in lateral earth pressures than in granular fill, of the order 0.2-0.4 times the undrained shear strength. But for such clays the more significant issue is likely to be lateral swelling pressures. For clays placed relatively dry, a relaxation in lateral stress has been observed immediately after compaction (Sowers et al., 1957 Symons et al., 1989). However, as rainwater enters the fill, swelling starts to occur. In situ determinations...

Rainwindinduced oscillations

A phenomenon experienced on a number of cable-stayed and arch bridges in recent years, vibrations have been witnessed when low wind speeds combine with light rain. Stays within polyethylene ducts are known to be the most susceptible to this effect. Rain-wind oscillations of the stays usually occur in the wind speed range of 7-20 m s. Below this range the rain rivulets do not form, while above this range the rivulets tend to be blown off by the wind before excitations occur. It has been...

Mean wind speed

Recording periods of between 10 minutes and 2 hours provide reasonably stable measurements of the mean component of the wind. In the UK a recording period of 1 hour at a height of 10 m is adopted. As previously highlighted, the mean wind speed varies with height from the ground due to drag at the earth's surface. A number of laws have been derived to describe this variation, the most popular of which is the logarithmic law adopted by Eurocode 1 Parts 1-4 (British Standards Institution, 2005)....

Definition of wind

Wind results from the movement of air particles in the earth's atmosphere. The energy causing this movement is derived from solar radiation coupled with the radiation of heat away from the earth's surface. This produces temperature differences and thus pressure gradients which in turn cause acceleration of air particles between areas of high and low pressure. Away from the earth's surface the pressure system is relatively stationary as the pressure gradients are balanced by the earth's...

Wind induced vibration

When considering the dynamic response of structures to wind there are two broad categories of mechanisms that may occur. Short-term variations in wind speed produce turbulent flow, or buffeting, that may result in resonant response of the structure. Excitation may also occur in smooth flow and these responses are categorised as aerodynamic instabilities. All bridges are subject to the wind, however some types are more susceptible to dynamic response than others. For many simple bridge types...

Conclusions

Reinforced concrete provides an efficient main material for a wide range of bridge deck types. It is also the only practical material for many elements of bridges which have steel or prestressed concrete main elements. In this chapter the types of RC deck have been considered and the principal design checks for reinforced concrete design reviewed. American Association of State Highways and Transportation Officials (2002) Standard Specification for Highway Bridges, 17th edition. AASHTO,...

Commercial Street Bridge Sheffield UK

The bridge carries an arterial tramway close to the Sheffield City centre (Figure 11). There were many constraints to the site which led to a tied arch solution that offered minimum depth of construction and an enhancing visual impact. All the main members are in steelwork. The segmental arch members are pinned at each end and are braced together over the central section. Each of the 1.6 m, deep steel edged beams tie their respective arch and are suspended by a series of 60 mm diameter solid...

Effects of seasonal deck expansion and contraction

Longitudinal movements in the bridge deck due to creep, shrinkage and temperature changes cause forces at bearing level on non-integral abutments. The magnitude of these forces depends upon the shear characteristics or frictional resistance of the bearings. The coefficient of friction of most bearings lies in the rangef 0.03-0.06. The frictional force is derived from the nominal dead load and the superimposed dead loads on the deck. Integral abutments do not have bearings, and therefore the...

Stressedribbon bridges

Several footbridges have been constructed utilising prestressed concrete as a 'stressed-ribbon' deck where the tendons are laid out between the abutments and a concrete deck constructed around them before additional prestress is imposed to compress the deck. Figure 64 shows the Kilmacanogue footbridge in Ireland where this technique was used to good effect.

Chippingham Street Footbridge Cycleway Sheffield UK

The Chippingham Street bridge carries a footway cycleway over a canal which passes through a steep-sided cutting 10.5m deep and 52 m wide at the top (Figure 4). The ground conditions were good with 1.5 m of fill overlying sandstone and mud-stone beds with a recommended safe bearing capacity of 600kN m2. The choice of steel rolled sections together with the simplicity of line and form, produced a structure which integrates well with its environment, offering an interesting focal point whilst...

In situ singlecell boxgirder bridges

In situ single-cell box girders such as the typical section shown in Figure 44 are used for a wide range of spans from 40 up to 300 m when haunched. The advantages are the efficient use of concrete and prestress and the flexibility in span arrangements, while the disadvantages include the labour-intensive activities on site and the long construction times needed for the larger structures. For spans up to 60 m a constant depth section with depth span ratio of 1 20 would typically be used, with...

Incrementally launched boxgirder bridges

Where the bridge alignment is straight or on a constant radius curve, either vertical or horizontal, launched single-cell box girders may be used to overcome access problems or to avoid obstructions at ground level. Commonly used for spans up to 60 m, the technique has occasionally been used for longer spans up to 100 m with the help of temporary piers placed to reduce the effective span length during launching. Deck depth must be constant for launching purposes, with the ratio to the launched...

Highstrength friction grip bolted connections

It is generally a requirement that for bridgework all bolted structural connections are made using high-strength friction grip (HSFG) bolts. These bolts, which are tightened up to achieve a specified shank tension, act by clamping together the plates to be joined, so that under normal loading conditions the applied forces are transferred through the connection by friction acting at the plate interfaces. High-strength friction grip bolts are manufactured to the requirements given in BS 4395...

Introduction Of Architecture Bridge

Structural steel is an extremely versatile material eminently suited for the construction of all forms of bridges. The material, which has a high strength-to-weight ratio, can be used to bridge a range of spans from short through to very long (15-1500 m), supporting the imposed loads with the minimum of dead weight. Steel bridges normally result in light superstructures which in turn lead to smaller, economical foundations. They are normally prefabricated in sections in a factory environment...

Wing walls

The primary function of the wing walls on an abutment is to contain the backfill material at the rear of the abutment wall and minimise settlement of the carriageway. The combination of soil containment and compaction of the backfill material may lead to high lateral earth pressures. Figure 10 Reinforced earth components (Clayton et al., 1993) Figure 10 Reinforced earth components (Clayton et al., 1993) Consequently, the horizontal forces acting on both the abutment wall and the adjacent wing...

Load distribution Introduction

Traffic loads on bridge decks are distributed according to the stiffness, geometry and boundary conditions of the deck. The deflection of a typical beam-and-slab deck under an axle load is shown in Figure 37. For a single-span right deck on simple supports with different stiffness in two orthogonal directions, it is possible, using classical plate theory, to determine the load distributed to each member. If the amount of load carried by the most heavily loaded member can be found then the...

Water

Rivers in flood represent a serious threat to bridges both from the point of view of lateral forces on the abutments, piers and superstructures and the possible undermining of the foundations due to the scouring effect of the water. The lateral hydrodynamic forces are calculated in a similar manner to those due to wind. Thus from (where vc is the velocity of flow in m s), if the density of water is taken as 1000 N m3 then the water pressure (as for wind). Values of CD for various shaped piers...

Precastin situ concrete composites

A bridge made of precast prestressed concrete beams forming the web and tensile flange with an in situ top slab constituting the compression flange uses these two types of concrete efficiently. This kind of structure usually avoids the extensive falsework normally associated with in situ concrete construction. For short spans in the 3-15 m range, the beams are often encased in concrete to form a slab. While this form may be relatively heavy it is comparatively simple to construct and the large...

Plates in shear

Figure 26 shows a plate panel loaded by in-plane shear along its edges. A perfect elastic plate will, as for compression, carry load by in-plane action alone prior to reaching its elastic critical stress. The plate will distort in-plane with stretching of one diagonal and shortening of the other, creating orthogonal tension and compression stresses. It is the compressive component of the stress state that causes buckling and hence the buckling mode is of a diagonal form as shown in the figure....

Ultimate strength in punching shear

Codes require a check on punching shear around concentrated loads or supports. In EC2, this is done on a section at 2 times effective depth, d, from the face of the loaded area. This section has no physical significance it is simply the distance at which the shear stress calculated for test specimens at failure matched the limiting shear to the codes. The actual failure cone extends further from the loaded area. Because of this, although the check is done on a surface 2d from the load, you can...

Z

The term Z is known as the elastic section modulus and is tabulated in section tables for steel members (see The Steel Construction Institute, 2007). The elastic moment capacity of a given section may be found directly as the product of the elastic section modulus, Z, and the maximum allowable stress. If the section is doubly symmetric, then the neutral axis is midway between the two extreme fibres. Hence, the maximum tensile and compressive stresses will be equal. For an unsymmetrical section,...

Connections

Bjorhovde R., Brozzetti J. and Colson A. (1987) Proceedings of Int. Conf. on Connections in Steel Structures. Elsevier Applied Science, London, Feb. Blodgett O. S. (1966) Design of Welded Structures. James F. Lincoln Arc Welding Foundation, Cleveland. CIRIA. (1981) Lack of Fit in Steel Structures. Report 87, CIRIA, London. Cullimore M. S. G. and Eckhart J. B. (1974) The distribution of clamping pressure on friction grip bolted joints. The Structural Engineer, 52, No. 5, 129-131. Hicks J. G....

Worldwide bridge damage observations

One of the earliest detailed and pictorial accounts of bridge failure is due to Milne (1892), where a description of the effects of the 'Great Earthquake of Japan, 1891' was given. This earthquake hit on 28 October 1891 and affected the prefectures of Gifu and Aichi and was felt over an area of approximately 90 000 square miles. The earthquake caused severe damage and some cases of collapse to bridges, such as the collapse of the masonry piers of the Kisogawa bridge and the total collapse of...

General design considerations

Lateral Torsional Buckling Bracing

Plate girders are fabricated by welding flanges to a web plate as shown in Figure 35. The flanges are generally significantly thicker than the web because of the lower buckling capability of one edge unsupported plates as described above. Occasionally the unsupported edges of the flange are themselves stiffened by an outstand but this is not often done in bridge design as it adds extra fabrication cost to the beam. If the girder is to be used compositely with a concrete deck, the top flange...

Web crippling

Occasionally bridge girders are subjected to significant local concentrated loading that can induce high localised com-pressive stresses in the web. A good example of this occurs if the girder is launched over a rolling support. In this case the web may be subjected to very severe local patch loading at sections which are not strengthened by transverse stiffeners. In such circumstances it is necessary to check the web for local web crippling, the resistance to which is a function of the load...

Interface connection

The connection of the two parts of the composite structure is of vital importance. If there is no connection then the two parts will behave independently. If adequately connected the two parts act as one whole structure, potentially greatly increasing the structure's efficiency. Imagine a small bridge consisting of two timber planks placed one on another, spanning a small stream. If the interface between the two were smooth and no connecting devices were provided the planks would act...

Construction joints

A series of horizontal and vertical construction joints is normally required to build an abutment wall in two to three stages. A horizontal joint at 100-150 mm above the base slab to form a kicker for the next lift of concrete is essential to achieve accurate construction of the main wall of a cantilever abutment or the individual columns in a spill-through abutment. A further horizontal joint is usually introduced at 100-150 mm above the bearing shelf to enable the curtain wall at the rear of...

Abutment design calculations

The primary function of an abutment wall is to transmit all vertical and horizontal forces from a bridge deck to the ground, without causing overstress or displacements in the surrounding soil mass. The abutment wall also serves as an interface between the approach embankments and the bridge structure, so it must also function as a retaining wall. The degree of interaction between a bridge deck and an abutment wall depends largely on the nature of the bearing supports, if provided. There is an...

Bankseats

Simple mass concrete or lightly reinforced sections may be used for abutment supports at the top of cuttings where the foundation level is close to existing ground level (Figure 3). This type of structure is relatively small, and is usually 'stepped out' in section to reduce the foundation pressure and confine the resultant force on the bankseat within the middle third of its base. Small wing walls may be conveniently hung from the back of the bankseat to contain the immediate area of backfill...

Barker R M Design Of High Way Bridges

Table 6 Table of distribution coefficients D D can be easily obtained from either pre-prepared tables or from a computer program, then the critical bending moment is soon obtained. Tables of distribution coefficients for different types of live loading and ranges of characterising parameters can be prepared using suitable software. Example of a pre-stressed concrete beam and reinforced concrete slab deck A reinforced concrete slab on pre-stressed concrete Y-beams will illustrate the method. The...

Tension field method within Eurocode 3 Part

While tension field behaviour has been described in the context of an individual shear panel, the behaviour of a girder web exhibits additional features. The diagonal tension field band that occurs after the critical buckling stress is reached anchors off both the top and bottom flanges and also off the transverse stiffeners on either side of the web panel being considered. The degree of anchorage is dependent on the transverse stiffness of the flanges as well as the adequacy of the stiffener...

Welded connection design

There are two types of structural weld in common use, namely butt welds and fillet welds. A butt weld is normally made within the cross-section of the abutting plates whereas a fillet weld is a weld of approximately triangular cross-section applied to the surface of the plates to be joined. When plates greater than about 5 mm thick are to be butt welded together, the plate edges will have to be prepared before welding in order to obtain a full penetration weld. Figure 71 shows typical butt...

Synchronous lateral excitation

On a number of pedestrian bridges with lateral and tor-sional deck natural frequencies below 1.5 Hz substantial vibration amplitudes have been observed. The loading effect has been found to be due to the synchronisation of lateral footfall within large crowds of pedestrians on the bridge. The mechanism of this so-called 'synchronous lateral excitation' is due to the fact that pedestrians find it more comfortable to walk in synchronisation with any initial lateral vibrations in order to maintain...

Brno Vienna Expressway Bridge at Rajhrad Czech Republic

The bridge carries a local road across the Brno-Vienna Expressway near the town of Rajhrad in the Czech Republic. The total length of the bridge is 110 m with a central arch span of 67.5 m (Figure 17). At an early stage in the design it was decided that, for aesthetic reasons, an arch bridge was the preferred solution. The designers considered four options (Figure 18) (Strasky and Husty, 1999) two concrete arches supporting a double-T concrete deck on single spandrel columns a narrow steel box...

The modular ratio

Differences between the strength and stiffness of the materials acting compositely affect the distribution of load in the structure. Stronger, stiffer materials such as steel attract proportionally more load than materials such as concrete or timber. In order to take such differences into account it is common practice to transform the properties of one material into that of another by the use of the modular ratio. At working or serviceability loads, the structure is likely to be within the...

Design of details Anchorage

With pretensioned strand, the force transfer into the concrete is achieved through bond between the two materials. At the end of the strand it slips into the concrete as the bond gradually builds up the force transferred, until the total force in the strand has been taken up by the concrete over a transmission length, Lt. With Fo 4 75 UTS and ci 5 30N mm2, then this length is defined as kt can be taken as 600 for plain, indented or crimped wire with a wave height of less than 0.15Dt, 400 for...

Beam and slab bridges

In recent years, in situ beam and slab structures have been less popular than voided slab forms, while precast beams have generally been prestressed. Reinforced beam and slab structures have therefore been less common. However, there is no fundamental reason why they should not be used and there are thousands of such structures in service. One of the disadvantages of a beam and slab structure compared with a voided slab or cellular slab structure is that the distribution properties are...

Qwp

Condition, where all the load is carried on the beam and the stresses are a combination of Figure 41(i) and 41(ii), and the theoretical 'instantaneous' condition where the full dead load and prestress is applied to the composite section. The stresses will creep from the as-built condition towards the instantaneous condition as indicated in Figures 41(iv) and 41(v) with the final stress at any level in the section being given by final as-built + (1 - e X inst - CTas-built) The loss of prestress...

H

Figure 78 Typical dimensions of a gravity retaining wall Figure 79 Bridge abutment resisting horizontal forces from deck (after Hambly, 1991) Figure 78 Typical dimensions of a gravity retaining wall in Figure 78. Lateral active earth pressures for design of low retaining walls are usually estimated using conservative design charts. Some designers also use equivalent fluid pressures to compute the active earth pressure as pa 7eqH in which 7eq equals the product of the minimum active earth...

Box girder design rules

The Eurocode rules for plated structures are published as a European pre-standard at the current time (2008) (Eurocode 3 Part 1.5). While having been in existence for a number of years, the rules within BS 5400 Part 3 are probably still the most comprehensive available in the context of complex stiffened plated elements. This section deals in some detail with the principles behind both the Eurocode Part 1.5 rules and the BS 5400 Part 3 rules presenting some of the main design equations....

Diaphragms

Diaphragms are generally used in the deck at points of support to transfer the load from the webs into the substructure below. Typical diaphragm arrangements are shown in Figure 31. For the arrangement shown in Figure 31(i), a truss analogy is normally used to model the force transfer from the webs into the bearings. To ensure that all the load is picked up and transferred on to the truss at the top of the webs, 'hanging reinforcement' needs to be provided in the form of vertical bars in the...

Construction sequence and creep analysis

The way the bridge is built affects the moments and shears generated in the structure and this needs to be fully taken into account during the design. The structure should be checked for strength and stability, and serviceability stresses assessed at each stage of construction with the final moments and shears derived to reflect the construction sequence. For example, Figure 24 shows the dead load bending moments in a four-span deck constructed in stages, with the final moments after creep...

Propped construction

Propping the steelwork prior to concreting can aid slender or non-compact sections. The majority of load is carried by the composite section immediately the props are removed. For most medium-span bridges, the cost of propping is likely to be larger than any saving in steelwork (from reduced bracing and top flange requirements). Consequently it is not often used. On larger-span bridges, the potential saving resulting from the use of propping may be more significant and is often worth...

Primary temperature stresses BD 3788

Determine the stresses induced by both the positive and reverse temperature differences for the concrete box girder bridge shown in Figure 42 (A 940000 mm2, I 102 534 x 106 mm4, depth to NA 409mm, T 12 x 10-6, E 34kN mm2). 1. Calculate critical depths of temperature distribution From BD 37 88 Figure 9 this is a Group 4 section, therefore h 0.3h 0.3 x 1000 300 > 150, thus h 150mm h2 0.3h 0.3 x 1000 300 > 250, thus h2 250mm h3 0.3h 0.3 x 1000 300 > 170, thus h3 170mm

Open abutments

The term 'open abutments' is often used to denote the type of end supports required to extend the central span of a bridge to create adjacent 'open side spans'. Two basic types of abutment are used in this situation. A mass concrete bankseat situated at the top of the slope containing a side span or a buried reinforced concrete or piled skeletal or 'spill-through' abutment founded at or below previous existing ground level beneath an embankment slope. In general, it is possible to choose...

Shear resistance of plate girders in BS 5400 Part

If the web of the girder is only stiffened with transverse stiffeners and there are no longitudinal stiffeners, the shear resistance is calculated using a tension field approach which is very similar to that adopted by Eurocode 3 above. If the girder has longitudinal stiffeners a completely different approach is adopted for the web design. This is described later in this chapter in the context of box girder bridge design. As for the Eurocode, the three components of response, namely critical...

Bracing of steelwork

For composite bridges constructed from steel beams or girders with concrete slabs cast on top, the construction Figure 25 Bracing types for steel-concrete composite construction. (a) Ineffective bracing, (b) U-frame bracing, (c) cross-bracing, (d) plan bracing Figure 25 Bracing types for steel-concrete composite construction. (a) Ineffective bracing, (b) U-frame bracing, (c) cross-bracing, (d) plan bracing stage is a critical area that needs careful consideration. The steelwork is relatively...

Stress concentrations

In welded steel bridges the fatigue performance of the entire structure is usually governed by the fatigue strength of the individual welds. Fatigue cracks will initiate and grow from both load-bearing and non-load-bearing welds. This is because the welding process causes metallurgical discontinuities together with physical changes in shape both of which cause local stress concentrations. Stress concentrations are also produced by notches, holes and any abrupt change of shape in a member which...

Pile support

Because of the limited differential settlements that can be tolerated by most structures, it is likely that many bridge substructures will be supported on piles. There are two key issues in pile design The selection of an appropriate type of pile for the ground and groundwater conditions, and taking into account local practice and plant availability. Design of the pile, to calculate allowable loads and estimate settlements. Many problems occur because of the use of an inappropriate pile type,...

List of contributors

Abdunur, Consultant Engineer, Paris C. Arya, University College London, London D. Bennett, David Bennett Associates, Old Harlow C. Birnstiel, Consulting Engineering, Forest Hills R. A. Broom, Atkins Global, Epsom P. Brown, Oxfordshire County Council L. Canning, Mouchel Consulting Ltd P. Clash, Clash Associates Ltd C. R. I. Clayton, University of Southampton, Southampton G. Cole, Surrey County Council D. Collings, Benaim Group, London S. Collins, Mouchel Consulting Ltd P. Cooper, Consultant...

Proceedings Of The Ice - Bridge Engineering Design Suspension Bridge

AASHTO. (1996) Standard Specifications for Highway Bridges, 16th edn. American Association of State Highway and Transportation Officials, Washington, DC. Aparicio A. C. and Casas J. R. (1997) The Alamilo cable-stayed bridge special issues faced in the analysis and construction. Proceedings of the ICE, Structures and Buildings, Nov. Atkins F. E. and Wigley P. J. (1988) Railway underline bridges developments within constraints of limited possession. Proceedings of the ICE, Part 1, 84, Oct....

Primary and secondary effects

When the prestressing tendons apply load to the structure the resultant forces and moments generated can be considered as a combination of primary and secondary or parasitic effects. For a theoretical beam with a concordant tendon arrangement no secondary moments are set up, but this rarely occurs in practice. The stage-by-stage construction sequence and envelope of loads applied to the structure inevitably result in a non-concordant prestress layout and secondary moments can be significant....

Design of web stiffeners in BS 5400 Part

The design of transverse web stiffeners has been dealt with in the context of plate girders above. The only significant difference is the inclusion of the longitudinal stiffener area (when present) which has been incorporated into Equation (32). The design of longitudinal web stiffeners is based on similar principles. The longitudinal stiffener is designed as a column spanning between transverse web stiffeners with an effective section comprised of the stiffener plus an effective width of web...

Other considerations Lack of fit

In an HSFG bolted connection, good 'fit-up' of the parent and cover plates is essential if a load-bearing connection is to be achieved. If this is not the case, and the joint faces are not flat and or not properly aligned, then some or possibly all of the prestress in the bolts will be used to bring the plates into contact with little or no bolt tension available to induce the friction resistance in the faying surfaces. Construction Industry Research and Information Association (CIRIA) has...

Anchor blisters

Figure 28(i) shows the additional reinforcement needed to tie the tendon into the main body of concrete where anchors are placed on blisters, or concrete blocks cast on the side of the concrete member. The bursting and spalling reinforcement quantities are calculated as for standard anchors, but the additional tieback reinforcement is required to prevent cracks occurring behind the anchor due to the tensile forces generated to achieve strain compatibility in the concrete around the blister or...

Interaction between shear and bending in BS 5400 Part

The basis of this interaction is not dissimilar to that in the Eurocode. It is, however, in the form of a multi-linear interaction diagram, rather than the curves of the Eurocode. The diagram is presented in the code as four linear equations represented by Figure 47. As for the Eurocode, significant levels of bending and shear are allowed to coexist with no interaction. In this context BS 5400 caters for slightly less interaction than the Eurocode. If the applied shear is less than half the...

Wind tunnel testing

Wind Tunnel Bridge Section Model

Wind tunnel testing is commonly undertaken for bridges with long or unusually flexible decks. BD 49 01 (Department of Transport, 2001a) provides guidance as to when the use of wind tunnel testing is likely to be required in order to properly understand the structure's aerodynamic behaviour. There are three main objectives for the use of wind tunnel testing. Firstly where bridge decks or piers do not conform to the standard cross-sections contained within design codes, wind tunnel testing is...

Historical note on bridge codes in Europe the USA and Japan

The history of European practice in seismic design is rather recent, and cases of bridge damage in European earthquakes are very few indeed. For Europe, the interest in seismic design of bridges arises from two main considerations, namely the potential for disastrous effects and the export market. With regard to the former, several thousand bridges in Italy are potentially subjected to considerable earthquake risk, while major projects for bridge construction are under way in Greece, among...

Freestanding wing walls

Free-standing wing walls are designed as a nominal cantilever retaining wall with a separate foundation from the main abutment. Differential settlement and tilting between the abutment and wings may occur. Hence, construction joints between the two structures require careful design to both permit and conceal the relative movements. To suit the local terrain, the wing walls can be arranged parallel to the abutment wall and this allows simple compaction of the backfill with no complications in...

Wisconsin Avenue Viaduct USA

The Wisconsin Avenue Viaduct in Milwaukee, Wisconsin is a 444-m long 11-span precast, prestressed concrete arch structure (Figure 9). The arches are provided by curved trough-shaped, precast post-tensioned arch segments that functioned as both load carrying structural members and as self-supporting permanent forms. The deck comprised pretension precast concrete beams that were framed into in situ concrete cross-beams. The use of precast concrete units mitigated against the construction...

Applied soil loadings

Bridge engineers have traditionally used the 'equivalent fluid' concept for calculating the earth pressures on an abutment, but selection of the appropriate intensity depends on the degree of restraint offered by the wall and the particular calculation being considered. Practice has followed retaining wall design. Therefore, in a situation where a wall can move by tilting or sliding and the backfill is a free draining granular material, active pressures are assumed. Provided that the abutment...

Cantilevered wing walls

A second approach to the design of wing walls parallel to the over-road is to use horizontally cantilevered wings. This form of construction is practical for lengths up to 12 m from the abutment, but care must be taken in designing the junction between the wing and abutment wall. The structure has the advantage of being founded on a common base so that it settles as one unit, but compaction of the backfill may be difficult around the wings. The rigid nature of this type of design encourages...

Construction effects

The construction of individual concrete columns is usually undertaken in two stages. A foundation slab with a construction joint is formed at 100-200 mm above the root of the column. For column heights of 5-10 m, the remaining height is then poured in one lift. Although the critical section for bending effects is theoretically at the root of a column, in reality the construction joints just above the base slab will constitute a plane of weakness. Flexural cracks are likely to develop at this...

L 1 L V V

Flat Angle Tee Bulb flat Trough Vee Figure 53 Range of stiffener cross-sections used in stiffened plating Figure 54 shows the configuration of a typical orthotropic deck, fabricated using open section stiffeners. The buckling modes for such a deck include buckling of the sub-panels between the longitudinal stiffeners, buckling of the stiffened flange between cross-girders and buckling of the overall flange with a longitudinal wavelength longer than the transverse stiffener spacing. In the...

Solid slab bridges Single spans

The solid slab is the simplest form of reinforced concrete bridge deck. Ease of construction resulting from the simplicity makes this the most economic type for short span structures. Solid slabs also have good distribution properties which makes them efficient at carrying concentrated movable loads such as wheel loads for highway bridges. However, above a span of around 10 m the deadweight starts to become excessive, making other forms of construction more economic. Solid slab bridges can be...

The history and aesthetic development of bridges

This chapter on the history and aesthetic development of bridges looks at the evolution and progress of bridges from their earliest conception by humans. Following a timeframe from the Palaeolithic period to the present all the various materials employed in construction are examined in relation bridge development. Aesthetic design in bridges - especially in the twentieth century is looked at in detail and the chapter ends with an essay on the search for aesthetic understanding in bridge design.

Wind loads BD 3788

Calculate the worst transverse wind loads on the structure shown in Figure 46. Assume that v 28m s span 33 m H 10m. S1 K1 1.0. From Table 2, S2 1.54 (i) Unloaded deck vt 28 x 1 x 1 x 1.54 43.13m s q 43.132 x 0.613 103 1.14kN m2 Thus Pt 1.14 x 97.02 x 1.4 154.84 kN (ii) Loaded deck vt 35 m s (maximum allowed in the code) From Table 5, d d2 thus b d2 9.52 2.94 3.24, and from Figure 5, CD 1.4. From Table 4, d d3 dL + slab thickness + depth of steel beams Pt 0.75 x 1.4 x (4.12 x 33) 142.76kN Thus...

Stiffened compression flanges in BS 5400

The main elements of a stiffened compression flange are shown in Figure 54 and associated buckling modes are shown in Figures 55 and 56. As indicated previously, a number of buckling modes have, in principle to be considered buckling of the sub-panels between the stiffeners buckling of the longitudinally stiffened panel between the cross-frames orthotropic panel buckling of the entire stiffened flange including the cross-frames local buckling of the elements of the stiffeners themselves. BS...

Design considerations

Many columns and piers in the UK were designed for bridges on the basis of working stresses and the principles contained in CP 114 (British Standards Institution, 1969) during the period 1955-1980. Permissible stresses for steel and concrete were given in BE1 73 (Department of Transport, 1973) and reference made to CP 114 for the permissible loads on short and long columns. Where the slenderness ratio was less than 15, then the column was treated as 'short'. As the slenderness ratio increases...

Analysis of masonry arch bridges

Having considered the behaviour of masonry as a material subjected to idealised loading conditions it is necessary to marry our knowledge of the behaviour of masonry arch bridges to the available mathematical models. It must be remembered that most masonry arch bridges were conceived as gravity structures for which mass and geometry were the design criteria. Certainly, the proportions passed down from antiquity had no thought of stress criteria and were probably based upon bitter experience....

Secondary loads Braking

Figure 16 Typical LM3 vehicle (in this case 1800 kN) This is considered as a group effect as far as HA loads are concerned, and assumes that the traffic in one lane brakes simultaneously over the entire loaded length. The effect is considered as longitudinal force applied at the road surface. There is evidence to suggest that the force is dissipated to a considerable extent in plan, and for most concrete and composite shallow deck structures it is reasonable to consider the loads spread over...

Ultimate strength in shear

Shear does not normally dictate the dimensions of the element. However, codes allow slabs (unlike beams) which do not have shear reinforcement and it is economically desirable to avoid shear reinforcement in these if possible. Use of links is particularly inconvenient in very shallow slabs, such as in box culverts or the deck slabs of beam and slab bridges, and many codes do not allow them to be considered effective. The shear strength rules can therefore be critical in design. Whereas flexural...

Abutment runon slabs and granular wedges

Bridge foundations and abutments are necessarily designed and constructed to restrict structural movements, since these would be associated with differential movements, and would induce additional bending moments in the structure. On the other hand, embankment fill adjacent to the deck can be expected to settle significantly (and perhaps a few per cent of the fill height). Without special measures, vehicle ride quality will be poor on the approaches to bridge decks, because of the disruption to...

L

Substituting these equations into equation (101) leads to the equation of motion of the flexural beam The above equation can be solved for beams with given sets of boundary conditions. Standard results are available in Figure 87 to compute the natural frequencies of uniform flexural beams of different supporting conditions. Methods are also available for dynamic analysis of continuous beams (Clough and Penzien, 1993). Beams can deform by flexure or shear. Flexural deformation normally dominates...

Assessment of masonry arch bridges

Top View Masonry Arch Bridge

It is vital that any assessment takes a holistic approach the materials, form of construction, loading, etc. should all be taken into account. All too often the assessment focuses upon the barrel with lesser regard to its interaction with the other elements of the bridge - when they, themselves, may be critical. In the UK, the current method of determining the load carrying capacity is embodied in the Department of Transport Department Standard BD 21 01 (Department of Transport, 2001) and...

Design of masonry arch bridges

Springing Stone Masonry Abutment

In considering the design of masonry arch bridges it is important to remember that there are over 40 000 examples in the UK alone. Most have already exceeded the Department of Transport's design life of 120 years and therefore must be considered as an archive of good practice and proportion. Traditionally, the span to rise ratio varies from 2 1 (semi-circular) to 10 1 but is usually in the range of 3 1 to 6 1 with the 'ideal' taken as 4 1. Clearly, the shape of the intrados is of great...

Classification of details

In order to undertake a fatigue assessment of a construction detail it is necessary to classify the detail into a particular strength group. These strength groups have been obtained from constant amplitude fatigue tests undertaken on a wide range of samples containing different welded detail types. Table 17 of BS 5400 Part 10 (British Standards Institution, 1980) gives a variety of construction details and indicates the prerequisites required to classify the relevant detail. The main features...

The early history of bridges The age of timber and stone

The bridge has been a feature of human progress and evolution ever since the first hunter-gatherers became curious about the fertile land, animals and fruit flourishing on trees on the other side of a river or gorge. Early humans also had to devise ways to cross a stream and a deep gorge to survive. A boulder or two dropped into a shallow stream works well as a stepping stone, as many of us have discovered, but for deeper flowing streams a tree dropped between banks is a more successful...

Pfp

Figure 37 Plate girder stiffened by longitudinal and transverse stiffeners stiffeners are often curtailed short of the tension flange in order to provide better fatigue resistance. This is shown in Figure 38. Such curtailment does not affect the buckling enhancement of the stiffening as the latter still provides out-of-plane bending support to the web plate. In longer-span girders it is possible to vary the cross-section in the longitudinal direction to match more closely the variation of...

Flexural members

One of the most common structural elements is a beam it bends when subjected to loads acting transversely to its centroidal axis or sometimes by loads acting both transversely and parallel to this axis. The discussions given in the following subsections are limited to idealised straight beams in which the centroidal axis is a straight line with shear centre coinciding with the centroid of the cross-section. The material of the beam is linearly elastic. The loads and reactions are assumed to lie...

Plan layout

It is often necessary to construct skew or curved bridges. It should be noted however that curvature in bridges complicates the design and analysis and leads to difficulties in uniformly distributing ductility demand (Burdette and Elnashai, 2008 Mwafy and Elnashai, 2007). It is often unconservative to analyse bridges with tight curvatures in 2D, hence a full 3D analysis is needed (Elnashai, 1996 Elnashai, 2004). Moreover, it is very difficult to quantify the degree of irregularity of a curved...

Lateral force resisting system

Monolithic Bridge System Moment Photos

The frame action resisting earthquake motion may be either single-column or multi-column structures, as shown in Figure 14 (Priestley et al., 1996). Single-column structures are easy to design and construct and are most suitable to situations where the demand along and across the bridge is similar. Also, since there is only one plastic hinge, response prediction is straightforward. It has several disadvantages however, such as low redundancy, high moment demand at the base, high seismic actions...

Earth pressures on spillthrough embankments

The so-called 'spill-through' or 'skeleton' abutment (Figure 2b) is in common use for multi-span bridges. In this form of structure the abutment columns are embedded in the embankment, which slopes down away from the crossbeam beneath the bridge deck. For this type of structure 1 the influence of the soil in front of the abutment should be considered and 2 soil arching and the effects of friction between the soil and the sides of the columns may be important. In the Building Research...