The report summarizes the results obtained from a comprehensive series of load tests on a full-scale portion of the building system. The test portion of the structure was constructed in the laboratory under provisions of plans and specifications prepared for field erection of the system. The test structure was one story in height and was part of a three-story-high building, chosen and loaded in a manner that simulated the structural response of the complete building subjected to dead, live, and wind loads. The report also presents results obtained from tests on components and materials used in the test structure. In addition to the evaluation of structural performance, significant information on structural interaction was derived from the data. 3. Notation and Conversion Units The following notation is adopted for use throughout this report: 1 lb (lbf) = 4.448 newton Pressure, Stress = 6895. newton/meter2 6.895×10 newton/meter" 1 psf = 47.88 newton/meter2 Some criteria for performance testing have been developed such as ACI 318[2] and N. Y. State Building Code [3]; however, these criteria are not sufficient for the evaluation of comprehensive building systems. The criteria developed for the purpose of this evaluation use some of the existing criteria, supplemented by new criteria where necessary. The performance criteria used in this report are presented and discussed in this section. First certain necessary definitions are developed; these are followed by Test Criteria and then Performance Criteria. Each Test and Performance Criterion is followed by a commentary. For convenience of reference, these Criteria are summarized in section 4.5. * Exactly 4.2. Definitions 4.2.1. Length of Members The length of horizontal members is taken as the distance between the center lines of their supports or the clear distance between supports plus the member depth, whichever is smaller. In the case of a cantilever beam, the "length" is taken as twice its actual length. 4.2.2. Deflections Deflection is the displacement of a point in a structure caused by the application of superimposed loads. The magnitude of the deflection at a point is the component of the displacement of the point in the specified direction, measured from its position before the application of the superimposed loads which caused the deflection. Horizontal deflections are measured in a direction parallel to the direction of the applied horizontal forces. Gross deflection is the total deflection of a point. Net deflection is the part of the gross deflection at a point which is attributable solely to the deformation of a structural member or assembly between its supports. Residual deflection is the deflection at a point after removal of superimposed loads, measured relative to the position of the point before application of the loads. 4.2.3. Superimposed Loads Superimposed loads are all loads applied to the test structure to simulate the dead, live, and wind loads acting on the real structure. 4.2.4. Failure Failure of the structure or any structural component is defined as one of the following: (a) An increase in deformation of an order of magnitude as defined in sections 4.4.1 and 4.4.3, occurring within 10 minutes without increase in applied load. (b) The inability of the structure to resist further load. (c) Sudden major cracking, major spalling, or structural collapse. 4.3. Test Criteria In order to satisfy the requirements for a This time limit was introduced in order to distinguish between long-term creep and a deformation occurring over a relatively short period of time. performance test, the following Test Criteria must be satisfied. 4.3.1. Model Selection A portion of the structure which is capable of simulating the response of the entire structure, and which will represent conditions providing the least margin of safety, shall be selected for testing. Foundation conditions shall be simulated in a manner representing the most adverse anticipated conditions that may exist in a complete structure in the field. Commentary on Criterion 4.3.1. A similar criterion is developed in ACI 318[2]; however, the emphasis in this paper is on the requirement of having a section of the structure which (1) will represent the performance of the entire structure, and (2) will represent this performance in a conservative manner. 4.3.2. Loading "Superimposed loads" shall be applied in a manner which will result in conditions equal to or more adverse or more adverse than the conditions in the full-scale structure and which provide the least margin of safety. Comentary on Criterion 4.3.2. Criterion 4.3.2 requires a simulation which is conservative. It is recognized that exact duplication of field conditions cannot be achieved and should not be attempted. Instead it is required that the test simulate superimposed loads in a manner which will provide the least margin of safety that may exist under any circumstances. provides a margin of 10 percent over the maximum lateral loads likely to occur under service conditions. There has been limited experience with high-rise apartment structures which indicated. that when such a structure is designed to permit horizontal deflection in excess of h/400 to h/500 under maximum service wind loads, discomfort and anxiety are experienced by some of the occupants under severe wind conditions. Although it is extremely conservative for low-rise structures, this deflection limitation is adopted here since a more comprehensive criterion has not been developed. 4.4.2. Horizontal Deflection Under Dead, Live, and Wind Load At a load level of 1.3 Dead + 1.7 Live + 0.8 Wind (1.3D + 1.7L + 0.8H), the horizontal deflection due to the superimposed load of 0.3D + 1.7L + 0.8H shall not exceed the following: Dh 0.002h. Commentary on Criterion 4.4.2. Even though the most critical loading with respect to horizontal deflections of a structure is in many cases a combination of minimum vertical and maximum lateral loads, maximum vertical loads combined with lateral loads may be more critical. This criterion imposes conditions which represent the highest loads which should cause no permanent structural damage. It would be unrealistically conservative to impose maximum lateral loads. A lesser lateral load is therefore adopted for this criterion, accounting for the low probability of simultaneous action of maximum vertical loads, combined with maximum wind forces. Commentary on Criterion 4.4.4. Structures should not suffer large irreversible deformations under loads which are lower than their ultimate design loads. It is therefore reasonable to require structures to resist superimposed loads up to 90 percent of their ultimate design loads without suffering significant irreversible deformations. Under most codes, 1.3D + 1.7L is about 90 percent of the ultimate design load. This is therefore the highest load which should be reasonably expected to cause no permanent structural damage. The deflection limitation in 4.4.4 (a) represents an extrapolation of the service load deflection limit of with an 480 additional allowance for creep deflection. Criterion 4.4.4 (b) is similar to criteria 4.4.1 and 4.4.2, which have been discussed earlier. Criterion 4.4.4 (c) requires 75 percent recovery of vertical deflections. This guards against structural systems which experience significant permanent sets in each cycle of loading that may lead to progressive incremental collapse. By permitting residual deflections of up to 25 percent of initial deflections, reasonable tolerances are provided for creep and system slack. The 75 percent recovery requirement is relaxed for very stiff structural で systems (dv < -), since there are in20,000t variably some small irrecoverable deformations in all structures. Criterion 4.4.4 (d) requires 75 percent recovery of deflections in excess of "net" deflections. These deflections are primarily due to deformations of columns and/or walls and this criterion provides reasonable tolerances for creep and system slack. Lower limits for recoverable deformations cannot be set in this case until further studies are conducted. 4.4.5. Ultimate Strength The structure or any portion thereof shall not fail at a load smaller than the following: (a) 1.25 (1.5D + 1.8L) (b) 0.9D + 1.4H. Commentary on Criterion 4.4.5. Criterion 4.4.5 (a) is for ultimate vertical loads. It is assumed that a structure may in extreme cases fail under loads which are as much as 20 percent below the average failure loads for similar structures (or of computed "ultimate" loads). In absence of a statistical sample of any size it is necessary to assume that if the laboratory sample has a strength of 1.0, the structure simulated by the sample may have a strength as low as 1 0.2 0.8. It is therefore required that the laboratory sample be 1 capable of withstanding a load of or 1.25 0.8 times the design ultimate load, which was taken. as 1.5D 1.8L. Criterion 4.4.5 (b) is tentatively adopted for ultimate lateral load, following the same philosophy with an ultimate load of 1.1H. 4.5. Summary of Test and Performance Criteria The preceding Test and Performance Criteria are summarized in this section for ease of reference. The criteria numbers remain unchanged. 4.3.1. Model Selection A portion of the structure which is capable of simulating the response of the entire structure, and which will represent conditions providing the least margin of safety, shall be selected for testing. Foundation conditions shall be simulated in a manner representing the most adverse anticipated conditions that may exist in a complete structure in the field. 4.3.2. Loading Superimposed loads shall be applied in a manner which will result in conditions equal to or more adverse than the conditions in the full-scale structure which provide the least margin of safety. 4.4.1. Horizontal Deflection Under Dead and Wind Load At a load level of 0.9D + 1.1H, the horizontal deflection due to the superimposed load of 1.1H shall not exceed the following: Dh 0.002h. 4.4.2. Horizontal Deflection Under Dead, Live, and Wind Load At a load level of 1.3D + 1.7L + 0.8H, the horizontal deflection due to the superimposed load of 0.3D + 1.7L + 0.8H, shall not exceed the following: Dh 0.002h. 4.4.3. Vertical Deflections Under Service At a load level of ID + 1L, the vertical deflection due to the superimposed load of 1L shall not exceed the following: dv < 480 4.4.4. Sustained Load Deflection At a load level of 1.3D + 1.7L sustained for 24 hours, deflections due to the superimposed 20,000t 80,000t The structure as erected and tested in the laboratory was a full-scale subsection of a modular building system. It was designed and constructed by Neal Mitchell Associates Inc. under the provisions of section 4.3.1 of the performance criteria. The plans and specifications were prepared by Neal Mitchell Associates Inc., and are dated 9-13-67. These should be referred to for detailed information. Some typical drawings from these plans were reproduced in this report and modified for illustrative purposes with the permission of Neal Mitchell Associates, Inc. This section of the report contains a description of the proposed structure, a description of the test structure as erected in the laboratory, and a discussion of the fidelity with which actual field conditions are simulated in this test. 5.1.1. Precast Components The precast components of the proposed structure are: (1) columns, (2) main beams, (3) tie beams, and (4) floor channels. Figure 5.2 illustrates an assembled structural frame which contains all the precast components. The frame is illustrated in more detail in figure 5.3. Figure 5.4 shows the erection of a frame. Figures 5.5 through 5.16 show detailed drawings of the precast components. Figure 5.5 is an isometric view of the main beam, tie beam, and column reinforcement at a connection. Figures 5.6 and 5.7 show typical column details. Main beam details and sections are shown in figures 5.8 and 5.9. Tie beam details are illustrated by figure 5.10. In accordance with the plans and specifications, main beams, tie beams, and columns are precast of cellular concrete with lightweight aggregate. The nominal wet density of the concrete is 95 lb/ft and specified nominal 28-day strength is 4,500 psi for lower-story columns and 3,500 psi for all other precast components. The wet density of this concrete is controlled by the addition of preformed foam at the time of mixing. Reinforcing bars are ASTM-A61 [5] (60 ksi) steel for primary reinforcement and ASTM-A15[6] (40 ksi) steel for stirrups, ties and other reinforcement. Column-beam connections and end details are illustrated in figures 5.11 through 5.15. Figure 5.11 is an isometric view of a disassembled connection. Tie beam end details are shown in figure 5.12; figures 5.13 and 5.14 show the column end detail, and figure 5.15 shows the details of an assembled connection. Written permission has been granted by Neal Mitchell Associates to include figures 5.3, 5.5, through 5.21 and 5.23. * All figures referred to in the text appear in the section beginning on p. 31. |