Major floor load of 370 psf Minor floor load of 280 psf (1D + 6.3L)

Column load of 60 kips on

four outer columns

(1D + 7L)

Column load of 0.9D South wind load of 10.5 psf (0.9D + 0.5H)

7. Instrumentation

A total of 98 electrical resistance instruments were used to monitor and record structural deformational behavior of the test model. These instruments are schematically located on figures 7.1 through 7.4.

Figure 7.1, an isometric view taken from the southwest of the model, shows the location of load measurement and wall deformation instruments. The instrument numbers correspond to channel designation of automatic data-acquisition equipment. Instrument No. 90, a semiconductor strain-gage pressure transducer, recorded the pressure of the hydraulic system used in simulating column axial loads. Instrument No. 91 recorded the magnitude of horizontal loads. Initially this instrument was a load cell, but was subsequently replaced (after Test No. 5) by a pressure transducer. Instrument No. 91 was interchangeable in location, depending on the direction of horizontal forces. Instrument No. 92 was one of several secondary pressure transducers monitored during the tests to check horizontal force accuracy. Instrument No. 93, a pressure transducer, recorded the magnitude of uniformly distributed floor loads applied by air pressure.

Instruments No. M1 through M7 represent measurement devices employed to check load applications. These instruments were not connected to the automatic scanner, but were manually monitored. M1 and M7 represent pressure transducers located in the associated hydraulic system, while M2 through M6 were load cells attached to the jacking rams. For each test, the pertinent load instrument and deformation linear variable differential transducers (LVDTs) were also recorded by an automatic X-Y plotter.

The LVDTs in figure 7.1 recorded diagonal deformations of dry wall panels over the gage lengths shown. Gages No. 52, 54, 55, 56, and 57 designate LVDT's having readout intervals

of 0.0001 in, while the remaining LVDT, gage No. 53, had an interval of 0.00001 in.

Figure 7.2 illustrates the northwest view of model instrumentation. Diagonal deformations were recorded by LVDT's No. 50, 51, 58, 59, 60, and 61, all with a 0.0001-in. readout interval. Horizontal deflections of the test structure were measured by LVDT's No. 43, 44, 45, 46, and 47 with a readout interval of 0.0001 in. Figure 7.3 is a plan view section showing vertical deflection transducers located under the second floor of the test structure. In addition, two transducers (No. 48 and 49) were positioned horizontally on the center main beam to record any differential movement relative to the ceiling slab. In general, the vertical transducer readout interval was 0.0001 in, excepting transducers located adjacent to columns read to the nearest 0.00001 in. Transducer readings were also checked by a dial gage deflectometer capable of reading 0.0001 in, which was read visually.

Figure 7.4 shows the location of 40 type A3 electrical resistance strain gages used to measure column concrete strains. The readout increment of these strain gages was 1 μin/in (i.e., 0.000001 in/in).

Calibration of load cells, pressure transducers, and deflection transducers was performed prior to testing of the structure.

Data-acquisition equipment included a 100channel and a 50-channel automatic electronic scanner and digital recorder. Instrument readings were taken at predetermined load increments. The output data was subsequently keypunched and reduced by electronic computer.

Dial gages were also used to check against possible slip of the test structure floor slab relative to the laboratory floor slab. No such slip was observed.

8. Results

A total of 18 load tests were carried out on the laboratory structure. Of these, 17 involved extensive measurement and recording of loads and structural deformation. The remaining test was run simply as a proof test on column capacity.

Tests No. 1 through No. 11 were performed. on the model of the total building system. Tests No. 12 through No. 18 (see section 6.3) were carried out on the system with wall panels removed.

Instrument locations are shown in figures 7.1 through 7.4. The instruments recorded loads and deformations for seventeen tests. Generally each instrument was read immediately after the attainment of the respective

increment of applied load. Reading and recording of data was in was in general accomplished through the use of an automatic data-acquisition system which recorded results in digital form on printed paper tape. Total acquisition time for each set of readings consisting of all data for one load increment was somewhat less than two minutes. The data was then manually key-punched onto cards, and was automatically reduced, analyzed, and plotted by electronic computer. Approximately 40,000 measurements were thus recorded.

Computer output consisted of a complete tabulation of results, and curves of measured deformations plotted against applied load. In all, more than 2000 curves were plotted. In addition to the data acquired by the automatic digital system, a continuous plot of critical deflection parameter versus applied load was maintained for all tests by an automatic X-Y plotter. This was used along with mechanical dial gages to provide a secondary and independent check on proper functioning of the automatic equipment.

After checking computer output for keypunching errors and malfunction of instrumentation, the results were reviewed to select the more significant information. The most pertinent results are presented and discussed in section 9; additional results are contained in Appendix A as figures. A.1 through A.77.

Each figure of Appendix A is a plot of applied load versus the model deformation as measured by the relevant instrument. The output channel number noted in the figure caption corresponds to the instrument number shown on figures 7.1 through 7.4.

The ordinate of each curve indicates the variable load. Load symbols are defined in section 3. The abscissa indicates deformation, where zero deformation is chosen prior to any load application. Thus in tests where an initial constant load is introduced, the abscissa indicates the deformation due to both the constant load and variable load.

All vertical deformations were measured relative to the structural test floor, thus beam. deflection measurements include column shortening, and slab deflection measurements include support movement.

Column concrete strain data have been excluded due to the erratic behavior of these strain gages. Column gages were located 6 in from column ends. Their erratic behavior is attributed to the proximity of joint connections and to the relatively large quantity of steel used in connecting column end hardware to longitudinal reinforcement.

9. Interpretation of Results

9.1. Introduction

The purpose of this section is to discuss the compliance of the structural system with the performance criteria in section 4, the structural behavior under loads, and the interaction of structural components.

It should be noted that all conclusions pertaining to structural performance are based on the structure as built in the laboratory and on erection methods and materials used therein. Variation in materials or erection methods may significantly affect structural behavior.

Data pertinent to the discussion in this section are presented in figures 9.1 thru 9.23.

9.2. Vertical Forces

Vertical forces were applied to the structure in the form of column loads (P), distributed floor loads between the columns (e), and distributed floor loads on the cantilever section of the second floor along the north side of the structure ('). (For location and magnitude of applied vertical loads, refer to fig. 6.1 and tables 6.1 and 6.2.)

Vertical loads were applied in all tests. In some of the tests they were applied along with horizontal loads in order to evaluate structural response to horizontal loads combined with vertical loads. Other tests were performed for the sole purpose of evaluating structural response to vertical loads. Details of all loading sequences have been discussed in section 6.

9.2.1. Structural Response to Vertical Loads

9.2.1.1. General

Figure 9.1 shows the load deflection history of the midspan of the center main beam under the application of a load of 1.3D 1.7L to the columns and main floor section. This figure also shows the effect of sustaining this load for 24 hr and the subsequent recovery of deflections 24 hr after removal of all loads. Deflections at one of the supports of this beam due to the same loading are also shown to permit evaluation of the order of magnitude of the "net deflections" as well as the column deflection. Examination of all test data indicates that from the point of view of magnitude of vertical deflections, this curve illustrates the most critical point in the structure.

"In this figure and several of the others used in this chapter, for the sake of clarity, individual data points and the data obtained during the several intermediate cycles of unloading and reloading have not been shown. However, these results are included on figures Al through A.77 of Appendix A.

The following observations can be made concerning midspan deflection of the center main beam under the application of a load of 1.3D 1.7L and its subsequent maintenance for 24 hr (fig. 9.1):

(1) The increasing load-deformation curve for the load application portion of the cycle was reasonably linear, indicating elastic behavior:

(2) The 24 hr creep amounted to less than 0.02 in, which is only 7 percent of the permissible deflection set forth as a performance criterion and about 13 percent of the total observed deflection;

(3) Observed recovery was 96 percent (note that most of the creep deflection was recovered).

Figure 9.2 shows the plot of midspan deflection of the center main beam during the application of a 370 psf load (1D+ 8.4L) to the main floor span after removal of the walls from the test structure (Test 16). This load was applied after the application of 1D + 1L to the columns. This test was designed to be a destructive test of the floor system of the structure; however, the capacity of the loading system (designed for 300 psf) was reached before failure of the test structure. The deflection at one of the beam supports is again plotted on this figure to illustrate the order of magnitude of the "net" deflections. Also shown is the curve for the center beam midspan deflection obtained in Test 9 before the removal of walls. In Test 9 the maximum applied floor load was 160 psf (1D + 3.5L). It is interesting to note the substantial reduction in stiffness against gross vertical deflection resulting from the removal of the walls from the system.

Two definite slope changes are evident in the curve for the midspan deflection of the structure without walls, one at 120 psf and one at 270 psf. A change in slope similar to that taking place at 120 psf is not evident in the curve for the structure with walls. It is felt that this change was probably due to some slippage at the beam column connection and was apparently of minor consequence in terms of structural performance.

The break which is evidenced at 270 psf is more marked. At this load, diagonal tension cracks were observed close to the beam supports (fig. 9.3). Since there are stirrups in the beam (figs. 5.8 and 5.9) and since the curve shows that the structure was capable of carrying substantial additional load, this point may represent a transfer of shear stresses to the stirrups. The structure was subsequently loaded to 370 psf (1D + 8.4L) without additional signs of distress.

Both figs. 9.1 and 9.2 illustrate the case of interior span loading (load "w" acting alone), since this appeared to be the more critical

loading configuration. The relative influence of these two loading patterns is illustrated by figure 9.4, which shows center main-beam midspan deflection for Test 9 with interior loading (e) alone, and Test 9A with interior and cantilever loading (w + ). As would be expected, the "" loading is more critical in terms of deflection; however, only slightly so.

9.2.1.2. Influence of Walls

The influence of the walls on structural response to vertical loads is illustrated in figures 9.2 and 9.5. Figure 9.2 compares deflections at midspan of the center main beam in Test 9 with walls, and Test 16 with walls removed. These tests had identical loading and the comparison is probably valid, although the structure may have been weakened somewhat before Test 16 by earlier tests. The location. at which deflections are compared in this figure reflects the behavior of the entire structure, since most members will make some contribution to the midspan deflection. These figures indicate that the structure with the walls removed had about twice the deflection of the complete structure.

Figure 9.5 compares deflections with and without walls at the position which is likely to be most sensitive to walls; namely, the center of the west main beam which rests on a fire wall. As expected, the influence of the walls. is even more marked in this case. The deflection at maximum load without walls is approximately 5 times the deflection with walls. It is thus evident that the walls contribute significantly to the support of vertical loads.

9.2.1.3. Slip Between Main Beams and Topping Devices which were capable of measuring the slip between the center main beam and the channel slabs were monitored during all tests. These were installed as a means of measuring any differential shear movement between the topping slab (which forms the compression flange of the main beams) and the precast element which forms the tension flange. In none of the tests was there any indication of relative slip between these two components. Neither was there any visual sign of relative slip, even in Test 16 (fig. 9.2) with a load of 1D + 8.4L.

9.2.1.4. Translation Due to Vertical Loads (Walls Removed)

This aspect of the structural response of the frame was investigated in Tests 12, 12A, 13, and 13A, in which the floor was alternately loaded over its main span alone (c) and its main span plus the cantilever span ( w′), with rollers oriented first to roll in the northsouth direction and then in the east-west direction. The results of these tests are shown in

where: dv vertical net deflection.

Under vertical loading of 1D +1L, the most critical vertical deflection in the test structure occurred at the midspan of the center main beam. Figure 9.4 illustrates test No. 9 plotting total vertical deflection at midspan of the center main beam together with total vertical deflection at one of the column supports of the same beam. The vertical net deflection will be the difference between the midspan deflection and the deflection of the beam support. Figure 9.4 illustrates that at the level of 1D + 1L the critical vertical net deflection was 0.04 in, which is considerably less than the permitted 0.30 in net deflection.

Criterion 4.4.3 was therefore satisfied.

(a) Under the vertical loading of 1.3D + 1.7L sustained for 24 hr the midspan of the center main beam exhibited the largest net vertical deflection (dr). This deflection was less than 0.10 in (see fig. 9.1). The net deflection (de) should be taken as the total deflection (Dr) less the support deflection. Unfortunately, during the sustained-load portion of this test, the instruments measuring the support deflection malfunctioned and there is thus no complete record of the beam support deflection. Thus, only the short-term portion of this deflection has been subtracted to obtain dr. The maximum measured Dr, which was 0.14 in, is considerably less than the 0.93 in allowed by Criterion 4.4.4 (a).

(b) The horizontal deflections, which were measured under vertical loads acting alone. both with and without walls, were extremely small. In all cases they were less than 0.08 in under 1.3D 1.7L on the floor and columns. (See figs. 9.6 and 9.7.) This is considerably less than the 0.19 in permitted by Criterion 4.4.4 (b).

(c) Figure 9.1 shows the residual deflection Der to be approximately 0.005 in, which is considerably less than the residual deflection permitted by Criteria 4.4.4. (c) and 4.4.4 (d), which is 0.03 in.

Criterion 4.4.4 was therefore satisfied.

9.2.2.3. Performance Criterion 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) = w 145 psf.

The structure was capable of carrying a load of 370 psf without experiencing failure (fig. 9.2).

Criterion 4.4.5 (a) was therefore satisfied.

9.3. Horizontal Forces

Horizontal forces were applied to the structure in the form of the horizontal loads H. Hs and Hs' (see fig. 6.1 and tables 6.1 and 6.2). Racking tests were conducted in the north and the east direction with and without walls. The results of these tests are described and evaluated in the following sections.

9.3.1. Horizontal Loads in the North Direction

In the north direction racking of the structure is resisted by the firewalls.

9.3.1.1. Racking Tests With Minimum Vertical Loads

These racking tests were conducted with a superimposed column load of 0.9D acting alone. The results of the racking test in the north direction are illustrated in figure 9.8. This figure shows lateral deflection measured at the level of the second floor of the test structure. Loads were applied to simulate a wind pressure of 25 psf acting from the south. It may be noted from this figure that while overall deflection was small (0.091 in), recovery was also small. Figure 9.9 shows the results of a later racking test which was carried to an equivalent of 60 psf wind load. These two tests are simultaneously plotted in figure 9.10* and show good agreement.

Figure 9.11 shows a plot of south wind load versus diagonal compressive deformation measured on one of the fire walls. The diagonal shown in this figure was measured over a gage length of 147 in. The resultant unit strain at a wind load of 25 psf is 0.000073 in/in and at a wind load of 60 psf it is 0.000250 in/in, which is extremely small. It is interesting to note from this figure that the recovery of the walls was good for all levels of load. No signs of distress were observed in the walls or other parts of the structure during Test 2 in which a wind load equivalent to 25 psf was applied. However, at the upper limit of Test 10 at a wind load equivalent to 60 psf, some distress appeared in the form of bowing out (buckling) in compression areas near the corners of the wall panels. These signs of distress disappeared upon removal of the lateral load. After removal of the walls all connections between the walls and the frame were found to be in good condition, showing no dislocation of screws or anchorage devices. During Test 10 there was some opening up of the joints between the columns and the wall panels in regions which would normally be subjected to tension by the development of diaphragm action in the walls. These openings were all less than 1 inch in width and tended to close partially upon removal of the load.