Seismic load, coefficients

A dynamic statistical approach is used to predict dynamic stresses in a hyperboloidal cooling tower due to earthquakes. It is shown that the configuration associated with one circumferential wave is the only one which is excitable by earthquake force and that the first mode of such configuration is dominant. An equivalent static load is calculated on this basis. Numerical data presented give coefficients for equivalent static loads, natural frequencies of cooling towers, and static stresses for a seismic load. 21 refs, cited. 

As to the large reservoir like Lenggu Hydro-power Project, the impact of seismic activity generally should be taken into account. For the earthquake condition simulation, the pseudo-static seismic analysis method was adopted. The moderate earthquake with exceeding probability to be 10 percent in the future 50 years was considered. Only horizontal seismic load was picked out and the input seismic coefficient was 0.167. The displacement contour and vectors after 1000 iteration steps are shown in Figure 7. Figure 8 shows... 

Generally, reinforcement serves to connect the leaves of the masonry wall, to allow for uniform distribution of vertical loads at floors and roof levels, to act as shear and flexural reinforcement for in-plane and out-of-plane seismic load transfer, and also to provide ductility, when reinforcement yielding precedes brittle failure of the masonry therefore, its beneficial role should be included in seismic analysis furthermore, for new constmction, when ductility is enforced by design, both elastic and inelastic methods of analysis are meaningful in seismic performance assessment, with a suitable response reduction coefficient applied in the expected seismic loads in this context, behavior factors up to 3.0, comparable to RC wall constmction, can be used in modem RM building design (EC6 2005). 

Peck et al. (1972) proposed closed-form solutions in terms of thrust, bending moments, and displacement under external loading. The lining response was a function of structure compressibility and flexibility ratios, in situ overburden pressure, and at-rest earth coefficient. To adapt to seismic loading, the free-field shear stress replaces the in situ overburden pressure and earth coefficient. The stiffness of the tuimel relative to the ground is measured by the compressibility (C) and flexibility (F) ratios. Those are the extensional stiffness and flexural stif iess of the medium relative to the lining. 

Rigid structures have short periods of vibration and are more susceptible to seismic destruction than flexible structures. For this reason, it is recommended that a seismic coefficient related to the vibration period of the tower be used in designing tall towers for earthquake loads. A tall, flexible structure capable of absorbing seismic shifts should not be penalized with the same seismic coefficient used for rigid structures such as masonry buildings that are more susceptible to failure from earthquakes. 

Designs for structures subjected to earthquake loads are empirical and are based on the analyses of structures that withstood earthquakes in the past. Earthquakes have periods of vibration, but the periods are complex. They are not simple harmonic vibrations in tall steel towers. Data on some past serious earthquakes are given in Table 4-5. The horizontal acceleration, a, produced by the shift of the earth crust divided by gravitational constant, gy gives the seismic coefficient, C or... 

Displacement Control Structures. In order to control the relative displacement between superstructure and substructure, both structures are connected at the bearing as shown in Fig. 12. The horizontal seismic design load is considered 3 times the vertical reaction due to dead load multiplied by a design horizontal seismic coefficient of 0.2 to 0.3. Furthermore, the maximum design displacement for unseating prevention is 0.75 xSE. 

N = number of equally spaced lugs W = weight of vessel plus contents, lb f = radial load, lb Fh = horizontal seismic force, lb Fv = vertical seismic force, lb Vh = horizontal shear per lug, lb Vv = vertical shear per lug, lb Q = vertical load on lugs, lb y, = coefficients... 

The result shows that the stability coefficient Kf of the Huanxi slope is greater than 1.0 when we use seismic dynamic load parameter values and the slope is in the basic stability state as a whole. 

According to the inversion results we can see that with the increase of the seismic peak acceleration, the slope stability coefficient gradually decreases, the relationship curve is approximate convex curve. That is to say the slope stability coefficient decreases quickly as the seismic peak acceleration increases. The point can be seen when the seismic peak acceleration is equal to 0.105 g, the slope stability coefficient is 1.003, which is unanimous with the stability coefficient gotten under the dynamic load strength test. 

The seismic coefficient is specified as a fraction, roughly 1/2, of the peak horizontal acceleration ratio a Jg at the crest of an earth dam because the lateral inertial force is applied for only a short interval during transient earthquake loading. ... 

The simplest way to do so is using the equivalent static lateral force method, even though its uses are limited by various conditions, related to the site and the stmcture itself and which are acknowledged and detailed below. Within this method, a seismic coefficient is applied to the mass of the stmcture to produce the lateral force that is approximately equivalent in effect to the dynamic loading of the expected earthquake. 

P-Delta or second-order effect is an instability phenomenon that results from the simultaneous actions of the lateral force and dead load. Seismic provisions require an evaluation of the structure stability under the anticipated lateral deflection by calculating a stability coefficient 6 for each story. The value of 6 is given by the following expression ... 

In the past, the Mononobe-Okabe method was used to calculate the seismic-induced dynamic earth pressures on underground structures. The method assumes the earthquake load is caused by inertial forces of the surrounding soil and calculates the load using soil properties and a determined seismic coefficient. This method is not applicable in the case of underground structures. 

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