W

Figure 27 Influence line for mid-span bending moment Influence lines for continuous beams Using the Miiller-Breslau principle, the shape of the influence line of any response of a continuous beam can be sketched easily. One of the methods for beam deflection can then be used for determining the ordinates of the influence line at critical points. Figures 28-30 show the influence lines for bending moment at various points of two-, three-and four-span continuous beams respectively. Plates and...

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...

Info

Precast Segmental Bridge Shear Key

Direction of CL Pier CL Pier CL Pier construction Direction of CL Pier CL Pier CL Pier construction Direction of CL Pier CL Pier CL Pier construction (i) Span-by-span erection CL Pier CL Pier CL Pier CL Pier CL Pier CL Pier CL Pier Direction of CL Pier CL Pier CL Pier construction (i) Span-by-span erection CL Pier CL Pier CL Pier CL Pier CL Pier CL Pier CL Pier Direction of CL Pier CL Pier CL Pier construction, . . Erect segments (ii) Balanced cantilever erection Temporary props Erect segments...

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 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...

Eighteenthcentury bridge building The Age of Reason

In this period, masonry arch construction reached perfection, due to a momentous discovery by Perronet and the innovative construction techniques of John Rennie. Just as the masonry arch reached its zenith 7000 years after the first crude corbelled arch in Mesopotamia, it was to be threatened by a new building material - iron - and the timber truss, as the principal construction for bridges in the future. This was the era when civil engineering as a profession was born, when the first school of...

Corrosion protection and ducting

Wires, bars and strand are generally used uncoated however, to protect the tendons during storage or to reduce friction losses during stressing they may be coated with soluble oil which is washed off prior to grouting the duct. Galvanised bars and strand are also available, as are epoxy-coated strand in some countries, although these Figure 8 Tendon coupler (courtesy of VSL International) Figure 8 Tendon coupler (courtesy of VSL International) Strand or bars Galvanised steel or plastic duct...

The past 200 years bridge development in the nineteenth and twentieth centuries

The Tyne Bridge Based Sydney Harbour

The industrial revolution which began in Britain at the end of the eighteenth century, gradually spread and brought with it huge changes in all aspects of everyday life. New forms of bulk transportation, by canal and rail, were developed to keep pace with the increasing exploitation of coal and the manufacture of textiles and pottery. coal fuelled the hot furnaces to provide the high temperatures to smelt iron. Henry Bessemer invented a method to Figure 8 US patent truss types (a) 1839 Wilton...

Cantilever abutment walls

Counterfort Type Retaining Walls

The survey by the Building Research Establishment (Hambly, 1979) confirmed that the T-section reinforced concrete cantilevered wall has been the most common form of construction for the solid wall type of bridge abutment in the UK up to that time and is still popular for longer bridges where integral abutments are not used. There are several variations on the basic theme to cater for different requirements. Propped cantilever walls are often used for right bridge decks with spans below 12 m,...

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this failure mode was considerably less well defined than those given above Figure 43 Parapet failure modes Hobbs et a ., 1998 B Vertical fracture line on wall centreline and to each side B Vertical fracture line on wall centreline and to each side However, it is reassuring that masonry parapets with a thickness of 400 mm or more and a minimum length of 10 m have the capacity to contain a 1.5 tonne vehicle, travelling at 60mph 100 kph impacting at an angle of 20 irrespective of mortar strength...

Reinforced earth abutments

A reinforced earth wall consists of modular facing panels normally of pre-cast concrete , earth fill and soil reinforcement Figure 10 . The wall is built by repetition of a set of operations at successive levels installing facing panels, placing and compacting earth fill, laying reinforcements and placing and compacting further earth fill. The sequences are repeated until the desired height is reached. The finished wall is able to resist lateral pressure by friction along the reinforcement BS...

Long bridges

The main effects on long, light bridges such as cable-stayed or suspension are galloping and stall hysteresis Random changes of speed and direction of incidence can cause dynamic excitation. Due to vortex shedding - alternately from upper and lower surfaces - causes periodic fluctuations of the aerodynamic forces on the structure. These are proportional to the wind speed, thus a resonant response will occur at a specific speed. In extreme cases witness the Tacoma Narrows Bridge in 1940 this can...

Alternative methods to the modified MEXE method

There are many situations where the modified MEXE method cannot be used or where the bridge fails according to the method. If such cases exist it may be deemed necessary to consider alternative methods of assessment. Several approaches have been developed in recent years. The masonry arch can be modelled as a pinned elastic arch and analysed using a suitable frame analysis or FE program. The analysis should be undertaken in two stages under dead load and under live loads. The ultimate live load...

Aesthetic design in bridges Introduction

Is it possible there is a universal law or truth about beauty on which we can all agree We can probably argue that no matter what our aesthetic taste in art, literature or music, certain works have been universally acclaimed as masterpieces because they please the senses, evoke admiration and a feeling of well-being. Music, literature and painting can appeal to an audience directly, unlike a building or bridge whose beauty has to be 'read' through its structural form, which has been designed to...

Fatigue fracture surface

Fatigue Failure Figure

A fatigue fracture surface normally exhibits two distinct regions typically a smooth flat area and a rougher area which forms the remaining part of the fracture cross-section as shown in Figure 75. Figure 75 Typical fatigue failure in a steel component ESDEP, 1998 Figure 75 Typical fatigue failure in a steel component ESDEP, 1998 The smooth region frequently exhibits concentric rings or 'beach marks' which surround the fracture point, and in addition, radial lines which tend to point towards...

Ultimate moment

As the applied bending moment on a prestressed beam increases, the compression on one side goes up while on the other side the concrete goes into tension. When the tensile strength of the concrete is exceeded, cracking occurs and the load is transferred either to the prestressing tendons or to any non-prestressed reinforcement present. As the applied moment further increases, the crack in the concrete opens and propagates across the section with a pure couple set up between the compression in...

Stay natural frequency

The natural frequency of a stay cable is dependent on the direction of motion. For in-plane vibrations the angular frequency, , is given by n 1, 2, 3, 4 etc. for 'taut' mode and 2, 2.86, 4, 4.92 etc. for sagging mode L 'straight' length of stay T tension force in stay w stay cable dead load per unit length If 8 L 3 EA wL lt 1 then taut mode governs 8 L 3 EA wL gt 4 2 then sagging mode governs vertical sag of cable at mid-span. Figure 14 Examples of stay friction dampers courtesy of VSL...

Free cantilever abutment walls

Bridge Abutment Wing Wall

Plane cantilever abutment walls are the most common form of construction for heights of 6-9 m and, in spite of the size, the main concrete wall is often poured in one lift. The wall stem generally ranges from 0.9-1.2m in width, so that it is wide enough to allow a person to climb into the reinforcement cage during construction. The overall width of the base will generally be 0.4-0.6 times the height and the toe may project 1.0-2.0 m in front of the wall. However, the physical dimensions and...

Plates under combined inplane stresses

The influence of plate slenderness and aspect ratio on the behaviour of a plate panel loaded in a combined stress state, e.g. uniaxial compression and shear, reflects the influence they exert on the individual load cases. In addition, there is an interaction between the individual buckling modes that might enhance or detract from the collapse loads under the individual stress components essentially dependent on whether the modes from the individual components are in sympathy. The elastic...

Rr nrxi

Figure 1 Types of section considered extend the economic span range of this type of structure to around 16 m or more. Above this span, and earlier for wider bridges, a lighter form of construction is desirable. One of the commonest ways of lightening a solid slab is to use void formers of some sort. The commonest form is circular polystyrene void formers. Although polystyrene appears to be impermeable, it is only the much more expensive closed cell form which is so. The voids should therefore...

In situ multicell boxgirder decks

Picture Multicell Box Bridges

Multi-cell box-girder bridges are similar to voided slabs with the voids occupying a larger proportion of the deck section. A typical arrangement is shown in Figure 42, which would have transverse diaphragms at each pier position. Concreting and formwork construction normally Figure 42 Typical multi-cell box girder arrangement Figure 42 Typical multi-cell box girder arrangement dictate a minimum depth of 1200 mm, and with depth span ratios of up to 1 25, the span lengths are normally greater...

Tendon couplers

It is possible to couple tendons together to assist in the stage-by-stage construction method frequently adopted. Figure 8 shows the coupler arrangement for strands, where a special anchor block is used to enable the tendon to be extended in to the next stage of concrete after it has been stressed against the previous stage. This arrangement can simplify the tendon layout and save the cost of a separate anchor. However, often the concrete section has to be widened to accommodate the coupler...

Ship and barge collision

Kinetic Architecture Timber

Where bridges are located in navigable waters they constitute a hazard to shipping and are thus vulnerable to damage or even destruction in the event of vessel collision. Whilst ship collisions with bridges are relatively infrequent they are generally serious, having significant human, economic and environmental consequences. On 9 May 1980 the Summit Venture, a 35,000 DWT bulk carrier, struck the Sunshine Skyway Bridge in Tampa, Florida, causing collapse of three spans and resulting in 35...

Hulme Arch Bridge Manchester UK

The bridge has a 52 m span, supported by 22 diagonal spiral strand cables 51 mm in diameter and hung from a single parabolic arch Figure 13 . The arch is made from a tapering trapezoidal steel box section coated in aluminium paint. The trapezoidal section varies from 3 m wide and 0.7 m deep at the crown to 1.6 m wide and 1.5 m deep at the springings. The arch rises 25 m above the bridge deck and is connected to each of the springing foundations using 32 high-tensile stainless steel 40-mm...

Anti Spalling Reinforcement

Spalling Reinforcement

The stress in the reinforcement 0.87 y should be kept to below 200N mm2 to control cracking while the bars should be placed as near to the end face as possible and anchored around the concrete edges. Where the anchor is positioned non-symmetrically on an end face, additional spalling stresses are set up and additional reinforcement is provided in the unsymmetrical direction such that A1 0.2 d - d2 di d2 Fo 0.87 y Equilibrium reinforcement This is provided to maintain the overall equilibrium of...

Precamber

Deflections of the concrete deck occur under the self-weight and from the weight of the permanently applied loads followed by further movements due to long-term creep of the concrete and losses in prestress. The deck must be cast and erected so that the theoretical profile is achieved upon completion. The adjustment made to the profile during casting to achieve the desired shape is called the precamber and this will be affected by the construction sequence and concrete properties. The creep...

Types of abutment

Abutment Capping Beam

The selection of appropriate abutments for a bridge should be made at the same stage as the choice of the deck superstructure. There are many types of abutment in use in the United Kingdom. A comprehensive survey by the Building Research Establishment Hambly, 1979 revealed a wide variation in the basic assumptions made in the design of these structures which is still valid today. Solid or full-height abutments Figure 2a are common, but are often not favoured on the basis of aesthetics, and can...

Ultimate torsion

Torsion does not normally govern the dimensions of the concrete members, but will require additional reinforcement in the section and is considered at the ultimate limit state. In determining the torsional capacity it is necessary to calculate the torsional shear stresses generated by the ultimate loads and where these stresses exceed Vtmin as given in Table 10 of BS 5400 Part 4 BSI, 1990 , then reinforcement is provided by means of transverse links and longitudinal bars. The stresses generated...

Analysis

Due to the way in which truss bridges transmit the imposed loads to the foundations, via axial tension and axial compression forces in the members, it is acceptable to analyse these structures as pin-jointed assemblies either as a two-dimensional plane truss, or preferably, as a three-dimensional space truss. This type of analysis assumes that member connections are pinned and consequently it is not possible for any of the truss members to attract moment or torsion forces. A two-dimensional...

Bridge construction and design Deck form

Deviator Concrete Block

Many factors affect the choice of the bridge type, the span arrangement and general layout, while prestressed concrete decks cover a wide range of construction forms with span lengths ranging from 25 m for single spans to over 450 m in cable-stayed bridges. For spans below 25 m, reinforced concrete is likely to be preferred, while for spans above 450 m steel or composite cable-stayed decks are used however, between these span lengths prestressed concrete often gives an economic, aesthetic and...

Ultimate shear

Shear need only be considered at the ultimate limit state, when the shear resistance must exceed the shear forces generated by the ultimate loads applied. The shear in the deck is checked adjacent to each pier and at regular intervals along the spans, and reinforcement, normally in the form of links, provided as required to give adequate resistance when combined with the concrete resistance. It is usual to assume that all the shear acts on the webs of a section and only the web resistance taken...

Serviceability limit state stress check

Longitudinal stresses in the prestressed deck are checked at each stage of construction, and throughout the structure's design life the stresses in the concrete under service loads must be within allowable limits. Typical allowable stresses in the concrete under service load are as follows 0.5fci lt 0.4fcu with triangular stress distribution, or 0.4fci lt 0.3fcu with uniform stress distribution. 0 N mm2 with permanent loads and normal live load 0.45 fc full loading and other effects on...

Large Mass Method

The 'Large Mass Method' is a convenient technique for applying earthquake time history to a bridge structural model. A very large point mass, M, is located below the foundations of the bridge piers and attached to it with 6DOF springs representing the foundation stiffness. The point mass itself is several orders of magnitude larger than the total mass of the rest of the model typically 106 . The acceleration time history, . t , is applied as a time-varying force function to the very large point...

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Figure 8 Typical spill-through abutment Figure 8 Typical spill-through abutment construction. The backfill spills between the legs and needs careful compaction around the columns to minimise long-term settlement. It is often used in the embankment situation where it is possible to obtain a suitable foundation at original ground level. In this case, it can form an economic alternative to a bankseat supported on piles driven through the embankment fill. A typical example of a spill-through...

HSFG bolt connection design

High-strength friction grip bolted connections designed to comply with BS 5400 Part 3 are not permitted to slip at the serviceability limit state. At the ultimate limit state, the connection is allowed to slip and the strength of the joint is governed by the bearing or shear capacity of the bolts, whichever is the lower. Clause 14.5.4.2 of BS 5400 Part 3 states that the design capacity of an HSFG bolt at the serviceability limit state is the friction capacity PD given by where 7m is the...