Reinforcement for beams of rectangular and T cross-section can be calculated. In calculation of longitudinal reinforcement bending moment about local axis Zloc and torsional moments are considered, but influence of longitudinal forces and bending moments in relation to local axis Yloc is ignored. In calculation of transverse reinforcement shear forces parallel to local axis Yloc a nd torsional moments are taken into account.
Reinforcement for beams can be calculated either from conditions of strength or from conditions of open crack width limitation (see parameter SSE).
Parameters SFA and EFA are considered only in calculation of transverse reinforcement.
In general case calculation of reinforcement for beams is carried out two times – according to strength conditions and according to conditions of open crack width limitation. In reinforcement calculations from conditions of strength design values of load have to be taken and in calculations from conditions of crack width limitation – characteristic (normative) load values are used. Both calculations can be carried out in one session with the use multiple analysis possibility of the program STAAD.Pro.
In most cases calculation of reinforcement is carried out with account only of a part of loadings. In such cases command LOAD LIST is used, in which numbers of loads considered in calculation are indicated. Number of permanent and long-term loads equal to parameter NLT must be included into the list of considered loads.
It has to be noted, that values of parameters DD1 and DD2 have influence not only on the width of opened crack but also in some cases, on design and normative reinforcement resistances.
Parameter BCL can be equal to any value of concrete compression strength class given in SNiP 2.03.01-84* and to any intermediate value as well.
It should be remembered, that accuracy of results of calculation of transverse reinforcement increases with the value of parameter NSE.
Parameters SFA and EFA are considered only in calculations of transverse reinforcement. Beam 1 is shown in Figure 2 with rigid intervals the lengths of which are: at the start of the beam 0.3m and at the end – 0.2m. In modeling of the beam the following command can be used.
MEMBER OFFSET 1 START 0.3 0 0 1 END -0.2 0 0
When command MEMBER OFFSET is used forces corresponding to the beam the length of which is equal to the distance between points a and b are calculated and then used in calculation of reinforcement. In such case it is necessary to take into account default values of parameters SFA and EFA equal to zero.
When command MEMBER OFFSET is not used forces corresponding to the beam the length of which is equal to the distance between points 10 and 11 are calculated and then used in calculation of reinforcement. In this case it is necessary to consider values of parameters SFA=0.3 and >EFA=0,2 in reinforcement calculation.
In both cases calculated quantity of transverse reinforcement will be the same. Calculated quantity of longitudinal reinforcement in the second case will be greater.
For beam the following output is generated:
method of calculation (according to conditions of strength or limitations of opened crack width);
length and cross-sectional dimensions;
distance from resultant of forces acting in bottom/top reinforcement to bottom/top edge of the section;
distance from the side edge of cross-section of the beam web to the centroid of longitudinal bars located at this edge;
class of longitudinal and transverse reinforcement;
assumed in calculations bar diameters of longitudinal and transverse reinforcement;
calculation results of longitudinal and transverse reinforcement (in two tables).
In nine columns of the first table the following results are presented:
|Section||distance of the section from the start of the beam, мм|
|As-||cross-sectional area of longitudinal reinforcement in the bottom zone of cross-section of the beam, if angle BETA=0°, or in the top zone, if BETA=180° , sq.cm|
|As+||cross-sectional area of longitudinal reinforcement in the top zone of cross-section of the beam , if angle BETA=0°, or in the top zone, if BETA=180° , sq.cm|
|Moments (-/+)||values of bending moments, determining cross-sectional areas of longitudinal reinforcement As- and As+ , kNm|
|Load. N. (-/+)||numbers of loading versions, determining cross-sectional areas of longitudinal reinforcement|
|Acrc1||short-term opened crack width*, mm|
|Acrc2||long-term opened crack width*, mm|
* Opened crack width is presented only in the case when calculation is performed according to conditions limiting opened crack width.
In ten columns of second table the following results are presented:
|Section||distance of the section from the start of the beam, mm|
|Qsw||intensity of transverse reinforcement, kN/m|
|Asw||cross-sectional area of transverse bars, sq.cm, if their step is 10, 15, 20, 25 or 30 cm|
|Q||value of shear force parallel to the local axis, kN|
|T||value of torsional moment, kNm|
|Load N.||number of loading version, determining intensity of transverse reinforcement|