Collapsing process simulations of timber structures under dynamic loading II: simplification and quantification of the calculating method
In a previous paper we presented the efficacy of the extended distinct element method (EDEM) on the collapsing process simulation of timber-frame structures. The results obtained were qualitative, and the need for quantitative simulation was pointed out. In this report, we improved our simulating programs with the aim of establishing a quantitative simulation by EDEM. For this purpose, the parameters of the frame members (beam or column) were determined by comparing the simulated results of four-point bending tests with experimental results. Other parameters of plywood and joint members were determined by simulations of two rail shear and slip tests of joint parts, respectively. Using these parameters we made simulations of the collapsing process of an actual-size plywood-sheathed wall and at the same time carried out the experiments under similar conditions. Simulated load–displacement curves of the plywood-sheathed wall were similar to those obtained in the experiments, and the sequence of failure at nailed joints of the simulation model gave good agreement with that of the experimental collapsing processes. Using these processes, we believe that we established a basic quantitative simulation method to test the collapsing process of timber-frame structures.
Collapsing process simulations of timber structures under dynamic loading I: simulations of two-story frame models
In this study we tried to develop an analysis program that can simulate the collapsing process of timber-frame structures under dynamic loading by adopting the extended distinct element method (EDEM). Using the EDEM, it is possible to trace the movement of any parts that were separated from unity after the failure of connecting elements, a property that fits our purpose well. As a preliminary study, simple two-story frame structures were modeled and examined by our program. Each model is an assembly of frame members composed of the EDEM elements. The spring elements of the joints have less rigidity than those of the frame members. Several models were analyzed under dynamic loading. The models varied in the configuration of bracing shear walls. Experiments with a one-ninth model were carried out under similar conditions, and the results were compared with the results from numerical simulations. Simulated results showed various collapsing processes corresponding to the arrangement of the bracing shear wall, and the simulated aspects gave good agreement with the results of the experiments under similar conditions.
Hygroscopic Expansion of some Casting Investments
CREDIT is generally given to Taggart1 for introducing the cast gold inlay to the dental profession. Although he realized that gold shrinks when cooled from molten state to solid state of room temperature, the investment available to him did not supply sufficient compensation. In 1910, Van Horn2 published a paper dealing with a method by which he obtained the compensation by means of wax expansion. The next major research in connection with this problem was the work of Coleman3 at the National Bureau of Standards. He determined the gold shrinkage to be 1.25 per cent and presented a casting technic with compensation values of quantitative nature. The total compensation for the gold shrinkage was obtained by the combination of the setting and thermal expansion of the mold. This procedure is the general practice followed at the present time for compensation. There are some disadvantages to this method. Skinner has indicated the difficulty of obtaining smooth castings and the improper compensation for the casting shrinkage.4 It has been found by Hollenback5 and Scheu6a that castings made at a high temperature are rougher than those made at a low temperature (450° C.), depending upon the great difference in thermal expansion between plaster of Paris and silica, which causes a poor union of the fine particles. This may also result in friability and there may be some warpage due to the differential expansion. A method which provides sufficient compensation at a low mold temperature is the hygroscopic casting technic.b Wilson7 showed that certain plasters expand as much as 0.0044 inch to the inch by taking up moisture from the air. With this information at hand, Scheula, b tested some commercial investment to determine what results the addition of moisture would have. He found6b: (1) All of the casting investments that were tested expanded. (2) The thicker the mix, the greater the expansion. (3) A mix with hot water expanded more than one with cold water. (4) The time at which the mix is placed in the water is of great importance. It was found that if the mix is placed in the water early, it would not expand so much as when placed in a little later. It was also found that if the mix was placed in the water after a certain time, it could not expand to the maximal amount. (5) The temperature of the water in which the mix is placed is important, for two reasons; (a) the temperature of the water controls slightly the expansion of the investment, and (b) water at a temperature of 1000 F. slightly softens the wax pattern so that the fine margins are not marred while expansion is taking place. The mix should remain in the water at least 20 minutes to obtain the full expansion, after which time no further expansion is obtained.