The assumptions made in this clause may be characteristic cube strengths of concrete are given in appropriate and the Engineer should adopt a in Part 7, and those which may be specified for more suitable method having regard to the nature of reinforced concrete are quoted in Table 5, together the structure in question.
Design should be based on the characteristic strength. The In the absence of a special investigation, the characteristic strengths of reinforcement are given plastic rotation capacity may be taken as the in the appropriate British Standards and are quoted lesser of: in Table 6.
Structures should be analysed in accordance with the recommendations 0. Redistribution but not less than 0 or more than 0. When analysing a cross 5. The effective span of a simply section to determine its ultimate moment of supported member should be taken as the smaller resistance the following assumptions should be of: made.
In both cases the strain at the outermost analysis. The effective length of a cantilever should be taken c The tensile strength of the concrete is ignored. In addition, if the ultimate moment of resistance, 5. In calculated in accordance with this clause, is less analysing structures, the full width of flanges may than 1.
For where Es is the modulus of elasticity of the steel. To ensure compression and the strains in the reinforcement, lateral stability, a simply supported or continuous whether in tension or compression, are derived beam should be so proportioned that the clear from the assumption that plane sections remain distance between lateral restraints does not plane.
The design charts that form The term 0. The value z should not be taken as greater For sections without compression reinforcement the than 0. A rectangular stress block of maximum depth 0. In no case should v exceed 0. Shear reinforcement should be provided as given in Table 7.
Where both top and bottom reinforcement is In Table 7: provided the area of As used should be that which is in tension under the loading which produces the v is the shear stress; shear force being considered.
These bars should be assumed to form u 1. The shear resistance at any vertical section should be taken as the sum of The spacing of the legs of links, in the direction of the vertical components of the tension and the span and at right-angles to it, should not compression forces cut by the section. Bars should exceed 0. In general, where the reinforcement, Asa, is required in the tensile zone torsional resistance or stiffness of members has not in excess of that required to resist bonding such been taken into account in the analysis of the that: structure, no specific calculations for torsion will be necessary, adequate control of any torsional cracking being provided by the required nominal shear reinforcement.
However, in applying this where clause it is essential that sound engineering Asa is the area of effectively anchored judgement has shown that torsion plays only a additional longitudinal tensile minor role in the behaviour of the structure, reinforcement see 5. Where torsion in reinforcement; a section increases substantially the shear stresses, V is the shear force due to ultimate loads at the torsional shear stress should be calculated the point considered.
In no case should the sum of the shear the face of a support, front edge of a rigid bearing or stresses resulting from shear force and torsion centre line of a flexible bearing. Torsion reinforcement should consist of rectangular Where this enhancement is used the main closed links in accordance with 5.
It should be calculated assuming that the closed links form a thin-walled tube, the shear stresses in 5. Where load is applied which are balanced by longitudinal and transverse near the bottom of a section, sufficient vertical forces provided by the resistance of the reinforcement to carry the load to the top of the reinforcement.
This reinforcement is additional to any requirements for shear or bending. Torsion does not usually decide the a Box sections. The torsional shear stress should dimension of members, therefore torsion design be calculated as: should be carried out as a check, after the flexural design. In such circumstances where reinforcement in excess of that required for flexure hwo is the wall thickness where the stress and other forces may be used in torsion.
Such sections should be that: divided into component rectangles for purposes of torsional design. This should be done in such a equation 10 way as to maximize the function C h max h 3min , where hmax and hmin are the larger and smaller dimensions of each component rectangle.
Each equation 11 rectangle should then be considered subject to a torque: where T is the torsional moment due to the ultimate loads; Ast is the area of one leg of a closed link at a Reinforcement should be so detailed as to tie the section; individual rectangles together.
Where the torsional shear stress in a minor rectangle is less than vtmin, AsL is the area of one bar of longitudinal no torsion reinforcement need be provided in that reinforcement; rectangle. Care should be taken in detailing links; to prevent the diagonal compressive forces in fyL is the characteristic strength of the adjacent faces of a beam spalling the section corner.
The longitudinal reinforcement should sL is the spacing of the longitudinal be positioned uniformly and such that there is a bar reinforcement. The diameter of the corner bars should be not less than the diameter of In equations 10 and 11, fyv and fyL should not be the links. In detailing the longitudinal reinforcement to cater b Rectangular sections. The torsional stresses for torsional stresses account may be taken of those should be calculated from the equation: areas of the cross section subjected to simultaneous flexural compressive stresses, and a lesser amount equation 9 a of reinforcement provided.
In the case of beams, the depth of the compression equation 10 a zone used to calculate the area of section subject to flexural compression should be taken as twice the where cover to the closed links.
Such allowance vtmin 0. For flanged beams, the 5. The sections of the flange which may be critical should be checked in shear stress, v, at any cross section in a solid slab, accordance with 7. Flexural cracking where in beams should be controlled by checking crack widths in accordance with 5. V is the shear force due to ultimate loads; 5. The ultimate space between links may be increased to d. If should not exceed the appropriate value given reinforcement is being provided to resist a in 5.
When made for the fact that the principal moment and considering this clause the dispersal of wheel loads reinforcement directions do not generally coincide. The critical section for calculating shear should be In voided slabs, the stresses in the transverse taken on a perimeter 1.
Where concentrated loads occur on a that the transverse section acts as a Vierendeel cantilever slab or near unsupported edges, the frame.
For a group of concentrated loads, adjacent loaded areas should be considered singly and in combination using the preceding recommendations. In solid slabs at least mm thick, where V lies between Vc and the maximum shear resistance based on that allowed for a beam in 5. Deflections may be calculated on perimeters progressively 0.
Cracking in slabs continues to be exceeded, further shear should be checked in accordance with 5. Shear 5. A reinforced concrete column is those places where the slab depth is greater than or a compression member whose greater lateral equal to mm.
Shear reinforcement may be in the dimension is less than or equal to four times its form of vertical or inclined links anchored at both lesser lateral dimension, and in which the ends by passing round the main reinforcement.
When openings in slabs and footings see Figure 6 le is the effective height in the plane of are located at a distance less than 6d from the edge buckling under consideration; of a concentrated load or reaction, then that part of h is the depth of the cross section in the plane the periphery of the critical section which is of buckling under consideration. The effective Where one hole is adjacent to the column and its height, le, in a given plane may be obtained from greatest width is less than one-quarter of the Table 11 where lo is the clear height between end column side or one-half of the slab depth, whichever restraints.
Where a more accurate evaluation of the effective height is required or where the end stiffness values are less than those values given in a , the effective heights should be derived from first principles.
Figure 6 — Openings in slabs The accommodation of movements and the method 5. The longitudinal ribs of articulation chosen for the bridge will influence between the voids should be designed as beams the degree of restraint developed for columns.
These see 5. The top flange of a rectangular voided exceed 40, except that where the column is slab should be designed to resist the punching effect not restrained in position at one end, the due to wheel loads see 5. Subclauses 5. When analysing a to 5. These methods may be assumptions should be made. In addition, for columns strains in the reinforcement are derived from the subject to applied bending moments the assumption that plane sections remain plane.
In both cases, the that if the column is slender the moments induced concrete strain at the outermost compression by deflection should be considered. An allowance for fibre at failure is taken as 0. In columns with end moments it is generally For rectangular and circular columns the following necessary to consider the maximum and minimum design methods, based on the preceding ratios of moment to axial load in designing assumptions, may be used. For other column reinforcement areas and concrete sections.
The design charts that form Part 3 of 5. A short column should be designed BS include charts based on Figure 1 and for the ultimate limit state in accordance with the Figure 2 and the assumptions in 5.
This is a nominal allowance for eccentricity due to construction tolerances. As2 is the area of reinforcement in the The following formulae based on a concrete stress other face which may be considered of 0. The following simplified formulae may be used, as appropriate, for the design of rectangular N is the ultimate axial load applied on column having longitudinal reinforcement in the the section considered; two faces parallel to the axis of bending, whether M is the moment applied about the that reinforcement is symmetrical or not.
This is the other face, derived from Figure 2 a nominal allowance for eccentricity due to and taken as negative if tensile; construction tolerances. A cross section of a slender column reinforcement about each axis, the section may be may be designed by the methods given for a short analysed for axial load and bending about each axis column see 5.
For slender equation 16 columns of constant rectangular or circular cross section having a symmetrical arrangement of reinforcement, the column should be designed to resist the ultimate axial load, N, together with the where moments Mtx and Mty derived in accordance Mx and My are the moments about the major with 5.
Alternatively, the simplified formulae x-x axis and minor y-y axis given in 5. For a column fixed in position at both ends where no For other column sections, design should be in transverse loads occur in its height the value of Miy accordance with 5. In no case, however, should Miy be taken as less than 0. A column When the overall depth of its cross section, hy, is less subject to uniaxial shear due to ultimate loads than three times the width, hx, a slender column should be designed in accordance with 5.
A and link reinforcement for the x-x slender column bent about both axes should be and y-y axis respectively derived in designed for its ultimate axial load, N, together with accordance with this clause. A column subjected to bending should be considered as a beam for the purpose of crack control see 5.
A reinforced wall is a vertical load-bearing concrete member whose greater lateral equation 22 dimension is more than four times its lesser lateral dimension, and in which the reinforcement is taken where into account when considering its strength. In other cases, this clause applies. Miy is the initial moment due to ultimate A reinforced wall should be considered as either loads about the y-y axis, including short or slender. In a similar manner to columns, a the nominal allowance for wall may be considered as short where the ratio of construction tolerances see 5.
It should otherwise be considered as lex is the effective height in respect of slender. The slenderness ratio The bending moment at right-angles to the wall is the ratio of the effective height of the wall to its should then be considered and the section checked thickness. The effective height should be obtained for this moment and the resulting compression or from Table When the wall is restrained in tension per unit length at various points along the position at both ends and the reinforcement wall length, using the assumptions of 5.
The critical the slenderness ratio may be up to A concrete walls. Forces and moments should be wall subject to uniaxial shear due to ultimate loads calculated in accordance with 4. For walls N is the ultimate axial load in newtons ; fixed to the deck, the moments should similarly be Ac is the area of the entire concrete section determined by elastic analysis.
Moments in the plane of a wall can be calculated from statics for the most severe positioning of the relevant loads. The cross section of the various clause. The moment per unit length calculated in accordance deflection of a reinforced concrete wall will be within with 5. The assumptions made when analysing acceptable limits if the recommendations given beam sections see 5.
Where plane of the wall. Where pockets are left for precast distribution of tension and compression along the members allowance should be made, when length of the wall. The resulting tension and computing the flexural and shear strength of base compression should then be combined with the sections, for the effects of these pockets unless they compression due to the ultimate axial load to are to be subsequently grouted up using a cement determine the combined axial load per unit length of mortar of compressive strength not less than that of wall.
This may be done by an elastic analysis the concrete in the base. Except where 5. The design shear is the algebraic sum the reactions to the applied loads and moments are of all ultimate vertical loads acting on one side of or derived by more accurate methods, e.
The analysis of a pile group or the application of shear strength of flat-slab bases in the vicinity of established principles of soil mechanics, the concentrated loads is governed by the more severe of following assumptions should be made.
The recommendations of 5. For b Punching shear around the loaded area, where columns and walls restrained in direction at the the recommendations of 5. The critical section in the design of an isolated base 1 Shear along any vertical section extending may be taken as the face of the column or wall. The The moment at any vertical section passing recommendations of 5. No redistribution of moments the head of a pile, the allowable ultimate shear should be made. Beam-and-slab bases should be d is the effective depth, to tension designed in accordance with 5.
Flat-slab sections should be designed to resist the total moments and shears at the sections Where av is taken to be the distance between the considered. In applying the recommendations width of the column and d is the effective depth, to of 5.
For greater 2 Punching shear around loaded areas, where widths, two-thirds of the area of reinforcement the recommendations of 5. The recommendations centred on the column. The critical Pile caps may be designed either by bending theory sections for local bond are: or by truss analogy taking the apex of the truss at a the critical sections described in 5. The deflection of bases need not be considered.
The location of all 5. When deciding on the the structure as a whole. In general, movement nominal overall size of a reinforced concrete joints in the structure should pass through the member regard should be given to the principles of whole structure in one plane.
Reference should be dimensional coordination. It should be borne in made to the relevant bridge authority regarding mind that absolute accuracy exists only in theory requirements for the design of joints.
The degree of tolerance should be as large as possible, without rendering the cover is that dimension used in design and indicated finished structure or any part of it unacceptable for on the drawings. The nominal cover should be not less than the size of the bar or maximum aggregate size, plus 5 mm; in 5. In all the case of a bundle of bars see 5. However, when reinforcement is located in equivalent area plus 5 mm.
In addition, it may be compressibility of these items and the surfaces necessary to specify concrete mix details to provide they bear on ; the required durability see Part 8. Subject to the reductions in member, this may affect the position of highly bond stress, bars may be arranged as pairs in stressed reinforcement at the opposite face of the contact or in groups of three or four bars bundled in member.
The consequent possible reduction in contact. In the design of a particularly critical except for bundles stopping at a support. Laps to one member, therefore, appropriate adjustment to the bar at a time in a bundle of three may be made, but effective depth assumed may be necessary. When it is necessary to there are no more than four bars in a bundle. Construction joints should generally be at 5. The dimensions of right-angles to the direction of the member and bars shown on the schedule should be the nominal should take due account of the shear and other dimensions in accordance with the drawings.
In stresses. If special preparation of the joint faces is other respects the guidance given in the technical required it should be specified.
The following: area of tension reinforcement in a beam or slab a in the bottom, or predominantly tensile, flange should be not less than 0. When, in a beam or column, part or all of the main reinforcement is required to resist compression, links or ties at least one-quarter the size of the largest compression bar The minimum number of longitudinal bars provided should be provided at a maximum spacing in a column should be four in rectangular columns of 12 times the size of the smallest compression bar.
All other bars or groups within a the characteristic strength of the reinforcement. For circular columns, where the wall unless the percentage of vertical reinforcement longitudinal reinforcement is located round the provided is at least 0. This vertical reinforcement provided by a circular tie passing round the bars or may be in one or two layers. The spacing of these links should not In a solid slab or wall where the main reinforcement exceed twice the member thickness in either of the is used to resist compression, the area of secondary two principal directions of the member and be not reinforcement provided should be at least 0.
The diameter should be not less than provided throughout the span to meet the one-quarter of the size of the vertical bars with recommendations given in 5. This The spacing of links should not exceed 0.
Links should enclose all tension In beams where the depth of the side face reinforcement. For the purposes of this code there are two types of deformed bar, as follows. Critical sections for local bond occur at the ends of simply supported members, at points where tension Type 1. A plain square twisted bar or a plain bars stop and at points of contraflexure. However, chamfered square twisted bar, each with a pitch points where tension bars stop and points of of twist not greater than 18 times the nominal contraflexure need not be considered if the size of the bar.
A bar with transverse ribs with a not exceed 0. To prevent bond failure the than 0. The anchorage bond stress, than 0. To prevent local bond failure see 5. The effective perimeter of a single bar may be taken as 3. The effective perimeter of a group of bars see 5. A link may be considered The lap length calculated in the preceding to be fully anchored if it passes round another bar of paragraph should be increased by a factor of 1.
In no than twice the bar size; case should the radius of any bend in the link be less b the clear distance between the lap and another than twice the radius of the test bend guaranteed by pair of lapped bars is less than mm; the manufacturer of the bar.
Continuity of reinforcement cover to either face is less than twice the bar size. Hooks, bends and other c sleeving see 7. Hooks and bends should e threading of bars, tapered threads. Such connections should occur, if possible, away The effective anchorage length of a hook or bend from points of high stress and should be staggered should be measured from the start of the bend to a appropriately.
When bars are lapped, the length of the lap should at least equal the anchorage 5. The bearing length derived from 5. The or is not assumed to be stressed beyond a point four length of the lap provided, however, should neither times the bar size past the end of the bend, need not be less than 25 times the smaller bar size be checked. A point at tension 1. Deformed bars, In addition, reinforcement should not be stopped in type 1 in a tension zone unless one of the following conditions tension 1.
Table 16 — Reduction factor One or other of these conditions should be satisfied for effective perimeter of a for all arrangements of ultimate load considered. These recommendations are not related to bar sizes but r is the internal radius of the bend; when a bar exceeds the maximum size of coarse 9 is the size of the bar or, in a bundle, the size aggregate by more than 5 mm, a spacing smaller of a bar of equivalent area.
A pair of bars in contact or a bundle of three or four bars in The stress should not exceed 1. At is the area of reinforcement in a 5. In all types of skew slab for which design moment and the direction of the the moments and torsions have been determined by tensile reinforcement, At, resisting that an elastic analysis, the reinforcement or moment. In b For flanges in overall tension, including tensile general, an orthogonal arrangement is zones of box beams and voided slabs, the design recommended.
The design crack width Special attention should be given to the provision of should then be calculated in accordance with b adequate anchorage of bars meeting the free edge at but may, in the case of a deck slab where a global an angle. The longitudinal steel will circular voids should not exceed twice the generally be placed parallel to the voids and it is minimum flange thickness. To prevent excessive cracking due 5.
The longitudinal to shrinkage and thermal movement, reinforcement steel will generally be in the form of prestressing should be provided in the direction of any restraint tendons in the precast units which are parallel to to such movements.
In the absence of any more the free edges. Ideally, the transverse reinforcement accurate determination, the area of reinforcement, should be placed at right-angles to the free edge, As, parallel to the direction of each restraint, should since this is the most efficient arrangement; be such that: however, in practice, the transverse reinforcement may frequently have to be placed at a different angle where or parallel to the supports.
Lightweight aggregate concrete may right-angles to the direction of the generally be designed in accordance with the restraint; recommendations of clause 4 and of 5. Only the section, Ac, i. The torsional properties for any particular type of aggregate can resistance and reinforcement for lightweight be established far more accurately than for most aggregate concrete beams should be established in naturally occurring materials and the Engineer accordance with 5.
Deflection of values taken from codes of practice or British lightweight aggregate concrete beams may be Standard specifications. The minimum cement contents Concrete grade given in Part 8 apply to lightweight aggregate 25 30 40 or more concrete. Values of vtu 3. The shear concretes may be taken from Table 5. When all resistance and reinforcement or lightweight aggregate in the concrete is sintered pulverized fuel aggregate concrete slabs should be established in ash, the related cube strength at other ages may be accordance with 5.
These values apply to most be used in place of Table 8 and the maximum shear other types of aggregate but reference should be stress, v, should be limited to the values given in made to the producer of the particular material Table With some aggregates used in rich mixes, there may be little increase in strength 5.
Deflection of lightweight beyond that attained at 28 days. The shear resistance and shear reinforcement for lightweight 5.
The 6. In clause 6, the design load effects see 2. In clause 6, when analysing sections, the terms 6. Other sequence and to the secondary effects due to methods may be used provided they can be shown to prestress particularly for the serviceability limit be satisfactory for the type of structure or member states. In certain cases the assumptions made 6. In clause 6 the design Engineer should adopt a more suitable method strengths of materials are expressed in all the tables having regard to the nature of the structure in and equations in terms of the characteristic question.
The b external tendons a tendon is considered characteristic cube strengths of concrete are given external if, after stressing and incorporating in in Part 7 and those which may be specified for the permanent works but before protection, it is prestressed concrete are quoted in Table 20, outside the concrete section ; together with their related cube strengths at other c lightweight aggregate.
Clause 6 follows the limit strength, fcu, except that at transfer the calculations state philosophy set out in clauses 3 and 4 but, as it should be based on the cube strength at transfer. The specified characteristic strengths of are given for both the ultimate and the prestressing tendons are given in: serviceability limit states. BS for high tensile alloy steel bars; In general, the design of class 1 and class 2 members is controlled by the cracking and concrete stress BS for high tensile steel wire and strand limitations for serviceability load conditions, but the including drawn or compacted strand complying ultimate strength in flexure, shear and torsion with section 3.
Guidance is given in 6. Complete structures 6. The definitions and limitations accordance with the recommendations of 4. In addition to limiting the The relative stiffness of members should slenderness of a beam see 5. Redistribution considered. This provided the following conditions are met.
The problem is complex and previous experience In the absence of a special investigation, the should be relied on in considering a particular case. The following assumptions may be made when considering design loads. For class 3 members transverse shears consequent on redistribution of elastic behaviour is deemed to exist up to the longitudinal moments by means of an compressive and hypothetical tensile stresses appropriate non-linear analysis.
The elastic modulus c Shears and reactions used in design are taken may be taken as that given in 4. The stress in the a Under service loads. The compressive stresses prestressing tendons under the loads given in 4. The stress at transfer should should not exceed the values given in be checked in accordance with 6.
Table Higher stresses are permissible for 6. The recommendations construction see 7. Design load in bending 0. No tensile stress, except as Design load in direct 0. The tensile stresses b At transfer.
The compressive stresses in the should not exceed the design flexural tensile concrete at transfer should not exceed the values strength of the concrete, which is 0. The limiting tensile stresses are given in Table Table 23 — Allowable compressive stresses at transfer 3 Class 3 members. For class 3 members in which cracking is allowed see 4. The hypothetical tensile stress 0. The cracking in prestressed concrete flexural members is dependent on the member depth, and the stress given by Table 25 should be modified by multiplying by the appropriate factor from Table For composite construction when flexural stresses given in Table 25 are not exceeded during construction, the full depth of the composite section should be used when using Table The within the tension zone and positioned close to flexural tensile stress in the concrete should not the tension faces of the concrete, these exceed the following values but see 7.
Members with by 4. Post-tensioned 2. An empirical approach for obtaining the stress in the tendons at failure 1. When analysing a cross fpu 0. In addition, the assumption that plane sections remain plane. In tendons will have an initial strain due to addition, the tendon will have an initial strain prestress after all losses. Calculations for shear are only whether initially tensioned or untensioned, and required for the ultimate limit state.
The provisions of this clause the stress-strain curves for prestressing tendons apply to class 1, class 2 and class 3 prestressed are given in Figure 3 and Figure 4 and those for concrete members. At any section the ultimate shear resistance of the In using the alternative method of analysis, the concrete alone, Vc, should be considered for the calculated strain due to the application of ultimate section both uncracked see 6. In addition, the reinforcement should be provided see 6.
The design charts in calculated from: BS include charts, based on Figure 1, Figure 3 and Figure 4, and the assumptions given a 5. In the absence of an of prestress at the section considered, assuming a analysis based on the assumptions given in 6. It may be the flange, may be obtained from equation The value of Vco is given by: fpb is the tensile stress in the tendons at equation 28 failure; x is the neutral axis depth; where d is the effective depth to tension ft is 0.
Prestressing a Where the position of a duct coincides with the position of tendons and additional reinforcement in the maximum principal tensile stress, e. Non-rectangular beams should be analysed using the assumptions given in 6. In flanged members where the centroidal axis where occurs in the flange, the principal tensile stress d is the distance from the extreme should be limited to 0.
This in which fpt is the stress due to component should be taken as positive where the prestress only at the tensile fibre shear resistance of the section is increased.
The ultimate shear resistance of a section cracked in flexure, Vcr, should be derived from the may be calculated using equation The ultimate shear resistance of a The value of Vcr calculated using equations 29 section cracked in flexure, Vcr, may be calculated and 30 at a particular section may be assumed to using equation For a section cracked in flexure and with inclined tendons, the component of prestressing where force normal to the longitudinal axis of the V and M are as defined previously; member should be ignored.
Mo is the moment necessary to produce 6. As t is the area of tensioned steel; As u is the area of untensioned steel; fpu t is the characteristic strength of the tensioned steel; fyL u is the characteristic strength of the untensioned steel; Vcr should be taken as not less than 0. A link stage under consideration or, in the case of should extend as close to the tension and the completed structure, after all losses. The links provided at a cross section should between them enclose all the tendons and additional depends on the type of interface; for reinforcement provided at the cross section and roughened and moistened segment faces a should be adequately anchored see 5.
The spacing of links along a beam should not exceed 0. When V exceeds 1. The suitable shear keys should be used. The design and lateral spacing of the individual legs of the links detailing of shear keys should be agreed with the provided at a cross section should not exceed 0. In no circumstances 6. Torsion does not usually decide the exceed the appropriate value given by Table 28 dimensions of members; therefore torsional design multiplied by bd, where b is as defined in 6. This is particularly relevant to some ungrouted ducts or two-thirds the diameter of the members in which the maximum torsional moment duct for grouted ducts; d is the distance from the does not occur under the same loading as the compression face to the centroid of the area of steel maximum flexural moment.
In such circumstances in the tension zone, irrespective of its characteristic reinforcement and prestress in excess of that strength.
Concrete grade The provisions of this clause apply to class 1, class 2 60 and and class 3 prestressed concrete members. Shear resistance with 5. When verification for post-tensioned segmental prestressing steel is used as transverse torsional structures is generally performed in the same way steel, in accordance with equations 10 and 10 a , or as for non-segmental structures, except that special as longitudinal steel, in accordance with consideration is required at joints, particularly equation 11, the stress assumed in design should be during the erection phase.
In addition to the check on the completed structure, The compressive stress in the concrete due to calculations for shear at joints should also be carried prestress should be taken into account separately in out for each discrete stage of erection. Reinforcement, if necessary, should be 6. Alternative methods provided in accordance with 6.
Prestressed concrete columns, where bending, shear and torsion may be used provided the mean stress in the concrete section imposed by that it can be shown that they satisfy both the the tendons is less than 2.
For flanged beams the should be considered. The tensile strength of sections of the flange which may be critical, should tension members should be based on the design be checked in accordance with 7. The additional reinforcement may 6. The usually be assumed to be acting at its design instantaneous deflection due to design loads may be stress 0. Members subject to axial tension should also be The total long term deflection due to the checked at the serviceability limit state to comply prestressing force, dead load and any sustained with the appropriate stress limitations of 6.
The jacking force may be accurate assessment is required see Appendix C. Where the permanent load the assessment of the friction losses. The analysis of prestressed slabs should determining the maximum initial prestress, to the be in accordance with 5. Attention should also be The design should be in accordance with 6. Allowance should be made when not stressed simultaneously, there is a progressive calculating the forces in tendons at the various loss of prestress during transfer due to the gradual stages in design for the appropriate losses of application of the prestressing force.
The resulting prestress resulting from: loss of prestress in the tendons should be calculated on the basis of half the product of the modular ratio a relaxation of the steel comprising the tendons; and the stress in the concrete adjacent to the b the elastic deformation and subsequent tendons, averaged along their length; alternatively, shrinkage and creep of the concrete; the loss of prestress may be computed exactly based c slip or movement of tendons at anchorages on the sequence of tensioning.
The loss of prestress in the tendons due to available, account should be taken of the properties shrinkage of the concrete may be calculated from of the steel and of the concrete when calculating the the modulus of elasticity for the tendons given losses of prestress from these causes.
For a wide in 4. System Humid Normal 6. For other ages of concrete at transfer, for other In special cases, such as tendons at high conditions of exposure, or for massive structures, temperatures or subjected to large lateral loads some adjustment to these figures will be e. Specialist literature should be consulted to Appendix C or specialist literature. When it is necessary to determine the loss of 6.
Calculation of the immediate loss of some stage before the total shrinkage is reached, it force in the tendons due to elastic deformation of the may be assumed for normal aggregate concrete that concrete at transfer may be based on the values for half the total shrinkage takes place during the first the modulus of elasticity of the concrete given in month after transfer and that three-quarters of the Table 3.
The modulus of elasticity of the tendons total shrinkage takes place in the first 6 months may be obtained from 4. For pre-tensioning, the loss of prestress in the 6. The loss of prestress is obtained from the product of the modulus of elasticity of the tendon see 4. Usually it is sufficient to assume, in calculating this loss, that the tendons are located at their centroid.
Since the actual losses of prestress due to exposure where the required cube strength at steam curing are a function of the techniques used transfer is greater than For lower values of cube 6. When the will cause a reduction in the prestressing force as maximum stress at transfer is half the cube the distance from the jack increases.
In addition, a strength, the values for creep are 1. In the absence of evidence established to the The figures for creep of the concrete per unit length satisfaction of the Engineer, the stress variation relate to the ultimate creep after a period of years. The extension of the place in the first month after transfer and that tendon should be calculated allowing for the three-quarters of the total creep takes place in the variation in tension along its length.
This is In applying the preceding recommendations, which directly proportional to the jack pressure, but it will are necessarily general, reference should be made to vary considerably between systems and should be Appendix C or specialist literature for more ascertained for the type of jack and the anchorage detailed information on the factors affecting creep.
Whether the for any movement of the tendon at the anchorage desired duct profile is straight or curved or a when the prestressing force is transferred from the combination of both, there will be slight variations tensioning equipment to the anchorage. The loss in the actual line of the duct, which may cause due to this movement is particularly important in additional points of contact between the tendon and short members, and for such members the the sides of the duct, and so produce friction.
The allowance made by the designer should be checked prestressing force, Px, at any distance x from the on the site. Where Po is the prestressing force in the tendon at circumferential tendons are tensioned by means of the jacking end; jacks the losses due to friction may be calculated e is the base of Napierian logarithms 2. The value of K per metre length in equation 31 should generally be taken as not less 6.
Other by trial and agreed with the relevant bridge values may be used provided they have been authority. The requirements of Part 7 should then established by tests to the satisfaction of the be satisfied. The transmission length is defined as the tendon. Such reduced values should be agreed with the relevant bridge authority. The bursting tensile force, Fbst, existing in an The development of stress from the end of the unit individual square end block loaded by a to the point of maximum stress should be assumed symmetrically placed square anchorage or bearing to be linear over the transmission length.
The end block also known as the Pk is the load in the tendon assessed in anchor block or end zone is defined as the highly accordance with the preceding paragraph; stressed zone of concrete around the termination points of a pre- or post-tensioned prestressing Fbst is the bursting tensile force.
It extends from the point of application of Table 30 — Design bursting tensile forces in prestress i. To see how to enable JavaScript, Please click here! Join Now Join Now. Life always offers you a second change. It's called tomorrow. You can't start next chapter of your life if you keep re-reading the last one. Success is the ability to go from one failure to another with no loss of enthusiasm. Only the people who dare to fail, will achieve big success. All glory comes from daring to begin.
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Other Standard. BS standard: Part 4 - Code of practice for design of concrete bridges. E-Coins fee :. Overview standard BS Steel, concrete and composite bridges. Code of practice for design of concrete bridges: This British Standard, a part of the BS series, gives recommendations for the design of concrete bridges. It contains much in common with BS which deals with the structural use of concrete.
After stating the objectives and requirements of design, particular recommendations are given for reinforced concrete, prestressed concrete and composite concrete construction.
Structural elements included are beams, slabs, columns and walls, bases, tension members and connections between precast concrete members. To download standard BS Steel, concrete and composite bridges. Code of practice for design of concrete bridges: Click the Download arrow icon. If the link fails, the document cannot be downloaded, please click on the Broken link to let us know.
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