Serviceability, limit state

The stochastic nature of variables is reflected in mean, standard deviation and type of distribution of relevant variables. An important notion is that most service-life approaches calculate the mean service life, that is the service life to be achieved with 50% probability. From the point of view of economy and safety, this is not acceptable. Depending on the severity of the adverse event occurring limit state), the failure probability should be (much) lower than 50%. Limit states can for example be the structure needs repair because concrete parts are falling off due to corrosion, or the structure collapses. The need for repair is termed a serviceability limit state (SLS). Collapse is termed an ultimate limit state (ULS). Serviceability limit states should have a low failure probability of the order of 1 100. Ultimate limit states involve safety (human lives) or loss of the structure (high economic damage) and must have a very low failure probability of the order of 1 10000. Failure probabilities like this are defined by e. g. EN 1990, Annex B and C [22]. As initiation of corrosion does not immediately have extreme consequences, a probability of failure has been proposed for this event of 1 10 [23]. 

Corrosion is thought to be initiated when the chloride content around the reinforcement exceeds a critical threshold value. This will generally be defined as a serviceability limit state (SLS), because the serviceability of the structure is compromised when repair is needed at relatively short notice. Assuming that the initial chloride content of the concrete is zero, the design equation for this SLS is given by ... 

It appears that the probability of corrosion initiation even with 70 mm cover depth is high (about 50 %) within fifty years. The probability of corrosion initiation after 12 y is about 1 % (corresponding to a serviceability limit state) for steel at 70-mm cover depth. The agreement with the results given in Table 11.4 is reasonable. 

SDWA Safe Drinking Water Act SLA serviceability limit state... 

This ultimate moment of resistance is greater than the design moment of 378 kN m and the section is, therefore, satisfactory for this ultimate limit state. However, it has to be checked for the stresses in the serviceability limit state. As for the ultimate load method, the second moment of area of the composite section is 7.01 x 10 mm and the elastic modulus of the steel beam alone is 949 cm , and thus the stage 1 steel beam stress is... 

It is rare for proof tests to be used in modern structural engineering unle there is some suspicion that something is wrong with the design or constructio As we shall see in Chapter 3 this has not always been the case. In the last centu before the extensive use of theoretical elasticity, proof tests were common. TI proof test may be considered as a sort of substitute prototype test if respon measurements are made and recorded. It may yield useful information abo system performance particularly in the serviceability limit states. As we w... 

The design bending moments for the serviceability limit state are obtained by using a different set of partial factors. C.P. 110 recommends that these should be unity and so the design bending moments in this case are 127.74 + 7.80 + 43.48 + 79.64 = 258.66 kNm. 

The water circulation was continued for 30 min so that thermal equilibrium was reached. Next, the structural load in serviceability limit state was applied to... 

In each scenario, the specimen was first loaded in a load-control mode to a prescribed level 100%, 75%, 50% of SLS (serviceability limit state) load, see Table 7.3. The load was then kept constant during the subsequent thermal loading process. The SLS-load, Psls> determined as follows ... 

Reliability can he defined as the probabilistic measure of assurance of performance with respect to some prescribed conditions (Krahk,J. 2009b). A condition can refer to an ultimate limit state (such as collapse) or serviceability limit state (such as excessive deflection and/or vibration). 

In general, FRP composites exhibit little or no ductile behaviour beyond a point of linear stress-strain behaviour of the material failure of the material may occur locally soon after this point has been reached. The design shonld take acconnt of this behaviour by ensuring that a serviceability limit state is reached prior to its ultimate limit state for the mode of failure being considered. 

Snch a serviceability limit state might be one of the following ... 

P(5) Serviceability limit states correspond to states beyond which specified service requirements are no longer met. 

Serviceability limit states which may require consideration include ... 

P(2) Three combinations of actions for serviceability limit states are defined by the following expressions ... 

For the purposes of global analysis at the ultimate limit slate and the serviceability limit state, to determine the forces in the elements forming the strucmre the section properties may be those corresponding to the nominal dimension of the said elements. 

Analyses carried out in connection with serviceability limit states should normally be based on linear elastic theory. 

Otherwise, provided stresses are kept within the limits corresponding to normal service conditions, the effects of creep and shrinkage need be taken into account only for the serviceability limit states, except where their influence on second order effects at the ultimate limit state is likeiy to be significant (see 2.5.1.4). 

Design limiting condition other than strength (usually serviceability limit state, SLS) (see 2.3.4)... 

Design procedure—serviceability limit state—deformation... 

P(2) For tension and bending at the serviceability limit state, the maximum combined tensile strain at any cross-section of the member shall not exceed the appropriate values for a tension member under similar environmental and service conditions. 

For compression and bending at the serviceability limit state, provided that all the conditions in P(3) and P(l) above are satisfied, only the limit state of deflection, due account being taken of additional deflections resulting from creep, need be considered. The limit state of local damage need not in general be considered for sections in compression and bending. 

P(l) The design of the laminate shall satisfy the conditions of 4.i at the ultimate limit state and of 4.2 at the serviceability limit state. 

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