Above the cracking load, the contribution of the concrete in tension may be taken into account using the assumptions given in item 4 of 3. BS part 2 deals with situations not specifically described in Part 1. Gives guidance on ultimate limit state calculations and the derivation of partial factors of safety; serviceability calculations, with emphasis on deflections under loading and on cracking. BS is cited by BS Stairs, ladders and walkways Code of practice for the design of helical and spiral stairs.
BS is cited by BS Lining of equipment with polymeric materials for the process industries - Specification for lining with rubbers.
BS is cited by BS Flat-bottomed, vertical, cylindrical storage tanks for low temperature service. Free version of MasterKey Concrete Beam Designer for the analysis and design of cantilever, simple, fixed and partialy fixed single span beams to BS and EuroCode 2. The degree of integration, simplicity of input and speed of design make BS is a British Standard for the design and construction of reinforced and prestressed concrete structures.
It is based on limit state design principles. Although used for most civil engineering and building structures…. BS deals with special circumstances and situations not specifically described in part 1.
Read our disclaimer here or here before you download the document from the website written above by clicking the below link. This new edition of a highly practical text gives a detailed presentation of the design of common reinforced concrete structures to limit state theory in accordance with BS Users of British Standards are responsible for their correct application.
Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 60, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued.
Sidelining in this document indicates the most recent changes by amendment. General 1 1. This part gives guidance on ultimate limit state calculations and the derivation of partial factors of safety, serviceability calculations with emphasis on deflections under loading and on cracking. Further information for greater accuracy in predictions of the different strain components is presented. The need for movement joints is considered and recommendations are made for the provision and design of such joints.
General guidance and broad principles relevant to the appraisal and testing of structures and components during construction are included. NOTE The titles of the publications referred to in this standard are listed on the inside back cover.
Methods of analysis for the ultimate limit state 2 2. Situations do, however, occasionally arise where the methods given in BS are not directly applicable or where the use of a more rigorous method could give significant advantages. In many cases it would be unreasonable to attempt to draft detailed provisions which could be relied upon to cope with all eventualities.
Much of this section is therefore concerned with developing rather more general treatments of the various methods covered than has been considered appropriate in BS The section also gives specific recommendations for certain less common design procedures, such as design for torsion. Design loads and strengths are chosen so that, taken together, they will ensure that the probability of failure is acceptably small. The values chosen for each should take account of the uncertainties inherent in that part of the design process where they are of most importance.
Design may be considered to be broken down into two basic phases and the uncertainties apportioned to each phase are given in 2. This phase is the assessment of the distribution of moments, shear, torsion and axial forces within the structure.
Uncertainties to be considered within this phase are as follows: a the magnitude and arrangement of the loads; b the accuracy of the method of analysis employed; c variations in the geometry of the structures as these affect the assessment of force distributions. This phase is the design of elements capable of resisting the applied forces calculated in the analysis phase. Uncertainties to be considered within this phase are as follows: a the strength of the material in the structure; b the accuracy of the methods used to predict member behaviour; c variations in geometry in so far as these affect the assessment of strength.
The partial factors given in section 2 of BS have been derived by calibration with pre-existing practice together with a subjective assessment of the relative uncertainties inherent in the various aspects of loading and strength.
From experience, they define an acceptable level of safety for normal structures. There may be cases where, due to the particular nature of the loading or the materials, other factors would be more appropriate. The choice of such factors should take account of the uncertainties listed in 2. Two possible approaches may be adopted; these are given in 2. When statistical information on the variability of the parameters considered can be obtained, statistical methods may be employed to define partial factors.
The recommendation of specific statistical methods is beyond the scope of this standard and specialist literature should be consulted for example, CIRIA Report [1].
This is the worst value that the designer realistically believes could occur it should be noted that, in the case of loading, this could be either a maximum or a minimum load, depending upon whether the effect of the load is adverse or beneficial. This value takes into account some, but not generally all, of the uncertainties given in 2. It is therefore still necessary to employ a partial factor but the value can be considerably reduced from that given in BS Absolute minimum values of partial safety factors are given in Table 2.
Table 2. The use of worst credible values is considered appropriate for many geotechnical problems where statistical methods are of limited value. Worst credible values of earth and water load should be based on a careful assessment of the range of values that might be encountered in the field.
This assessment should take account of geological and other background information, and the results of laboratory and field measurements. In soil deposits the effects of layering and discontinuities have to be taken into account explicitly. NOTE Methods of deriving earth pressures from these parameters can be found in the relevant code of practice.
When several independent parameters may affect the earth loading, a conservative approach is to use worst credible values for all parameters simultaneously when deriving the earth loading.
If significantly different values have been adopted, a more rigorous treatment of the SLS may be necessary see section 3. Analysis can only lead to superior results to the methods suggested in BS where the influence of the reinforcement is taken into account.
It follows that more rigorous or non-linear methods are only useful for checking designs or for use in an iterative procedure where the analysis is used as a step in the refinement of a design carried out initially by simpler methods.
It is to be assumed that the material strengths at critical sections within the structure i. If this is difficult to implement within the particular analytical method chosen, it will be Licensed Copy: University of Bath Library, University of Bath, 30 July , Uncontrolled Copy, c BSI acceptable, but conservative, to assume that the whole structure is at its design strength.
Characteristic stress-strain curves may be obtained from appropriate tests on the steel and concrete, taking due account of the nature of the loading. In the absence of test data, the following may be used. Concrete is assumed to have zero tensile strength. For concrete, Figure 2. The tensile strength of the concrete may be taken into account up to the cracking load. Above the cracking load, the contribution of the concrete in tension may be taken into account using the assumptions given in item 4 of 3.
The load combinations given in section 2 of BS should be considered. The partial safety factors may be taken from section 2 of BS or derived in accordance with 2.
Where the effects of creep, shrinkage or temperature are likely to affect adversely the behaviour for example where second order effects are important , it will be necessary to consider what part of the loading should be assumed to be long-term. It is acceptable, but conservative in such cases, to consider the full design load as permanent.
Any method may be adopted that can be demonstrated to be appropriate for the particular problem being considered e. However, when the design relies on the torsional resistance of a member, the recommendations given in 2.
As area of longitudinal reinforcement Asv area of two legs of closed links at a sectiona C torsional constant equals half the St. Venant value for the plain concrete section fyv characteristic strength of the links G shear modulus hmax larger dimension of a rectangular section hmin smaller dimension of a rectangular section sv spacing of the links Licensed Copy: University of Bath Library, University of Bath, 30 July , Uncontrolled Copy, c BSI T torsional moment due to ultimate loads vt torsional shear stress vt,min minimum torsional shear stress, above which reinforcement is required see Table 2.
Venant value calculated for the plain concrete section. The St. Venant torsional stiffness of a non-rectangular section may be obtained by dividing the section into a series of rectangles and summing the torsional stiffness of these rectangles.
The division of the section should be arranged so as to maximize the calculated stiffness. This will generally be achieved if the widest rectangle is made as long as possible. T-, L- or I- sections are divided into their component rectangles; these are chosen in such a way as to maximize h3 h in the following expression.
Box and other hollow sections in which wall thicknesses exceed one-quarter of the overall thickness of the member in the direction of measurement may be treated as solid rectangular sections. NOTE For other sections, specialist literature should be consulted. Recommendations for reinforcement for combinations of shear and torsion are given in Table 2.
The clear distance between these bars should not exceed mm and at least four bars, one in each corner of the links, should be used. Additional longitudinal reinforcement required at the level of the tension or compression reinforcement may be provided by using larger bars than those required for bending alone. The torsion reinforcement should extend a distance at least equal to the largest dimension of the section beyond where it theoretically ceases to be required.
Where the torsional shear stress in a minor component rectangle does not exceed vt,min, no torsion reinforcement need be provided in that rectangle.
Where a more accurate assessment is desired, the equations given in 2. I second moment of area of the section le effective height of a column in the plane of bending considered lo clear height between end restraints! There may, however, be cases where there are key elements as defined in 2. Details of such cases are given in 2. A horizontal member, or part of a horizontal member that provides lateral support vital to the stability of a vertical key element, should also be considered a key element.
For the purposes of 2. The reaction should be the maximum that might reasonably be transmitted having regard to the strength of the attached component and the strength of its connection. At each storey in turn, each vertical load-bearing element, other than a key element, is considered lost in turn.
The design should be such that collapse of a significant part of the structure does not result. If catenary action is assumed, allowance should be made for the horizontal reactions necessary for equilibrium. The length of wall considered to be a single load-bearing element should be taken as the length between adjacent lateral supports or between a lateral support and a free edge see 2.
For the purposes of this subclause, a lateral support may be considered to occur at: a a stiffened section of the wall not exceeding 1. Serviceability calculations 3 3. The purpose of this section is to provide further guidance when the first of these approaches is adopted.
In addition this information will be of use when it is required not just to comply with a particular limit state requirement but to obtain a best estimate of how a particular structure will behave, for example when comparing predicted deflections with on-site measurements. If a best estimate of the expected behaviour is required, then the expected or most likely values should be used. In contrast, in order to satisfy a serviceability limit state, it may be necessary to take a more conservative value depending on the severity of the particular serviceability limit state under consideration, i.
Failure here means failure to meet the requirements of a limit state rather than collapse of the structure. It is clear that serviceability limit states vary in severity and furthermore what may be critical in one situation may not be important in another.
Guidance on the assumptions regarding loads and material values are given in 3. This shortcoming can in many cases be at least partially overcome by providing an initial camber.
If this is done, due attention should be paid to the effects on construction tolerances, particularly with regard to thicknesses of finishes. This shortcoming is naturally not critical if the element is not visible. NOTE These values are indicative only. These values also apply, in the case of prestressed construction, to upward deflections. All elements should be detailed so that they will fit together on site allowing for the expected deflections, together with the tolerances allowed by the specification.
Loss of performance includes effects such as excessive slope and ponding. Where there are any such specific limits to the deflection that can be accepted, these should be taken account of explicitly in the design. Excessive accelerations under wind loads that may cause discomfort or alarm to occupants should be avoided.
NOTE For guidance on acceptable limits, reference should be made to specialist literature. Unless partitions, cladding and finishes, etc. NOTE For further guidance reference should be made to specialist literature. For members that are visible, cracking should be kept within reasonable bounds by attention to detail.
As a guide the calculated maximum crack width should not exceed 0. For members in aggressive environments, the calculated maximum crack widths should not exceed 0. Where cracking may impair the performance of the structure, e.
For prestressed members, limiting crack widths are specified in section 2 of BS Generally, for best estimate calculations, expected values should be used. For calculations to satisfy a particular limit state, generally lower or upper bound values should be used depending on whether or not the effect is beneficial. The actual values assumed however should be a matter for engineering judgement. For loads that vary with time, e. Generally, in serviceability calculations both best estimate and limit state it will be sufficient to take the characteristic value.
When calculating deflections, it is necessary to assess how much of the load is permanent and how much is transitory. The proportion of the live load that should be considered as permanent will, however, depend on the type of structure. Where a single value of stiffness is used to characterize a member, the member stiffness may be based on the concrete section. In this circumstance it is likely to provide a more accurate picture of the moment and force fields than will the use of a cracked transformed section, even though calculation shows the members to be cracked.
Where more sophisticated methods of analysis are used in which variations in properties over the length of members can be taken into account, it will frequently be more appropriate to calculate the stiffness of highly stressed parts of members on the basis of a cracked transformed section.
The modulus of elasticity may be corrected for the age of loading where this is known. Attention is, however, drawn to the large range of values for the modulus of elasticity that can be obtained for the same cube strength. It may therefore be appropriate to consider either calculating the behaviour using moduli at the ends of the ranges given in Table 7. Reference may be made to Section 7 for appropriate values for creep and shrinkage in the absence of more direct information.
Item a corresponds to the case where the section is cracked under the loading considered, item b applies to an uncracked section. Under short-term loading the modulus of elasticity may be taken as that obtained from 3. Assessment of the stresses by using a requires a trial-and-error approach. Calculation by means of a computer or programmable calculator is straightforward.
In assessing the total long-term curvature of a section, the following procedure may be adopted. NOTE In assessing the transformed steel area, the modular ratio should be as defined above. Ss is the first moment of area of the reinforcement about the centroid of the cracked or gross section, whichever is appropriate. These are as follows. Because the dead load is known to within quite close limits, lack of knowledge of the precise imposed load is not likely to be a major cause of error in deflection calculations.
Imposed loading is highly uncertain in most cases; in particular, the proportion of this load which may be considered to be permanent and will influence the long-term behaviour see 3. Considerable differences will occur in the deflections depending on whether the member has or has not cracked. Finishes and rigid partitions added after the member is carrying its self-weight will help to reduce the long- term deflection of a member. As the structure creeps, any screed will be put into compression, thus causing some reduction in the creep deflection.
The screed will generally be laid after the propping has been removed from the member, and so a considerable proportion of the long-term deflection will have taken place before the screed has gained enough stiffness to make a significant contribution. If partitions of blockwork are built up to the underside of a member and no gap is left between the partition and the member, creep can cause the member to bear on the partition which, since it is likely to be very stiff, will effectively stop any further deflection along the line of the wall.
If a partition is built on top of a member where there is no wall built up to the underside of the member, the long-term deflection will cause the member to creep away from the partition. The partition may be left spanning as a self-supporting deep beam that will apply significant loads to the supporting member only at its ends. Thus, if a partition wall is built over the whole span of a member with no major openings near its centre, its mass may be ignored in calculating long-term deflections.
A suitable approach for assessing the magnitude of these effects is to calculate a likely maximum and minimum to their influence and take the average. Deflections may be calculated directly from this equation by calculating the curvatures at successive sections along the member and using a numerical integration technique. Alternatively, the following simplified approach may be used: equation 11 where l is the effective span of the member; 1 is the curvature at mid-span or, for cantilevers, at the support section; rb K is a constant that depends on the shape of the bending moment diagram.
As the calculation method does not describe an elastic relationship between moment and curvature, deflections under complex loads cannot be obtained by summing the deflections obtained by separate calculation for the constituent simpler loads. A value of K appropriate to the complete load should be used. Table 3. The usual formulae for the end deflection of cantilevers assume that the cantilever is rigidly fixed and is therefore horizontal at the root.
In practice, this is by no means necessarily so, because the loading on the cantilever itself, or on other members to which the cantilever connects, may cause the root of the cantilever to rotate. There are two sources of root rotation which may occur. First, rotation of the joint in the frame to which the cantilever connects see Figure 3. This problem will require attention only when the supporting structure is fairly flexible.
Secondly, even where the cantilever connects to a substantially rigid structure, some root rotation will occur. This is because the steel stress, which is at a maximum at the root, should be dissipated into the supporting structure over some length of the bar embedded in the support. To allow for this, it is important to use the effective span of the cantilever as defined in 3. If Table 3. Before they crack, slabs will behave substantially as elastic, isotropic slabs.
As soon as cracking occurs, the slabs become anisotropic, the amount of this anisotropy varying continuously as the loading varies, and so a reliable determination of the moment surface for the slab under any particular load is not normally practicable.
Deflections of slabs are therefore probably best dealt with by using the ratios of span to effective depth. However, if the engineer feels that the calculation of the deflections of a slab is essential, it is suggested that the following procedure be adopted. A strip of slab of unit width is chosen such that the maximum moment along it is the maximum moment of the slab, i.
0コメント