Load-bearing Structure and External Wall
Vertical tolerances between beams and slabs
Horizontal tolerances between columns and walls
Openings
± 20 mm
± 20 mm 1) or ± l / 600 max. 60 mm
± 25 mm
l = clearance 1) More stringent values may be required for columns and walls that support prefabricated parts, depending 15 on the length tolerance of the supported component and the required bearing length.
to the service load. This should be established in close consultation with the client. If in doubt, the bending members must be analysed in the cracked state under the critical load and the analysis must take into account the long-term effects of shrinkage and creep of the concrete, so that, even in this final situation, no strains are imposed on the secondary structural elements. The vertical loads of the facade itself, for example self-weight, fitting out, imposed service loads and their application points represent further input parameters for the calculations. Fig. 18 shows the recommended maximum allowable deformations in accordance with DIN EN 1992-1-1 [15].
Width, height (edge length), opening 16
Design dimensions [m]
Limit deviations [mm]
Up to 1.00 m
± 2 mm
Over 1.00 m
± 0.2 % of the design dimension maximum ± 5 mm
modern structural engineering software solutions. The increasing variety of numerical modelling techniques available means it is relatively simple to calculate deformations in the cracked State II using the finite element method (FEM). The calculations are routinely carried out for conventional concrete structures and hybrid construction. In order to arrive at reliable deformation tolerances for the reinforced concrete structure, the designer must focus particularly on State II. The results of the calculation must be verified by the structural engineer for the project. Parametric Study
A parametric study [16] that was carried out as an aid to the designer evaluates the edge deformation of a slab span. This allows the designer to make a preliminary assessment of whether a proposed column or wall grid will result in acceptable
DIN EN 1992-1-1 also offers the option of precambering the formwork by a maximum of l/250 to partially or completely compensate for the eventual sag. A maximum value for the deformation of f ≤ l/500 is recommended for the edges of slabs to which the timber panel construction elements forming the facade are connected. Deformation calculations for the uncracked State I can be performed using the theory of elasticity. Analyses for the cracked State II are increasingly performed using
Deformation [f]
cracked State II are much larger than those in the uncracked State I. Accurate estimates of deformation are difficult to make. Often the normative level of load is not achieved or the material exhibits greater stiffness than the standard predicts. Precise input parameters characterising the individual concrete-specific shrinkage and creep behaviour are also difficult to define for a given set of circumstances. Some scatter applies to these parameters, which means the designer has to rely on limit value considerations. The deformations for State I can be adopted as the lower limit value. The maximum expected deformations are calculated assuming State II. The probable deformations will be somewhere between these two limit values. Fig. 17 shows that deformation f based on the input parameters load and the actual material resistances is subject to stochastic scatter and can also increase further during the service life due to shrinkage and creep. Deformation calculations are often based on engineering judgement. The normative load level is usually on the safe side in relation to the imposed load in service. To be able to accurately calculate deformations, the imposed load applied should be the one that most closely corresponds
17
er Upp
limit
14 Definition of the dimensions of timber panel construction elements 15 Building shell tolerances in accordance with DIN EN 13 670 16 Limit deviations for walls in accordance with DIN 18 202-3 17 Probability of the calculated value of the deformation f shown in relation to time t 18 Recommended maximum allowable deformations in accordance with DIN EN 1992-1-1
e
valu
II) tate re S u p ( alue ly v Like e valu mit li r e Low te I) (Sta
t=0
Time [t] t=∞
18
Determining factor
Maximum sag
Consideration of appearance and serviceability for slabs and beams
l /250
Damage of adjacent components caused by deformations
l /500
27
