Proposed instrumentation of Commerce Court for research into the effects of wind on tall buildings by CBR/NRC

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Proposed instrumentation of Commerce Court for research into the

effects of wind on tall buildings by CBR/NRC

DIVISION OF BUILDING RESEARCH 534

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PREPARED BY _{W. A. Dalgliesh} CHECKED BY W. R. S. APPROVED BY R.F.L.

..QAIS April 1969

PREPARED FOR the approval of: Canadian Im.perial Bank of Commerce; Page and

Steele, Architects; Weiskopf & Pickworth and C. D. Carruthers and Wallace, Consultants Limited.

SUBJECT PROPOSED INSTRUMENTATION OF COMMERCE COURT FOR

RESEARCH INTO THE EFFECTS OF WIND ON TALL BUILDINGS BY DBR/NRC

The owners and designers of Commerce Court, to be built in Toronto, have indicated a willingness to allow some measurements and studies to be made on the building by the Division of Building Research as part of its research into wind effects and perforITlance of tall building s.

The generosity of this offer and its appropriateness to the work of the Division on high-rise building design is acknowledged and greatly appreciated. Similar co-operative field projects with the owners

(Canadian Im.perial Bank of COITlITlerce) and the designers (Page and Steele, Architects; Weiskopf & Pickworth and C. D. Carruthers and Wallace, Consultants Limited, Structural Engineers):;.; have already re suIted in significant advance s. It is ｡ｮｴｩ｣ｩｰ｡Ｚｴｾ､［

that

the pre sent

proposal will lead to further substantial improveITlents in our understanding of the behaviour of tall, slender buildings in response to wind loading.

The objectives for measurements of wind effects are as follows: 1. Gathering of field data on ITlagnitude and distribution of wind

pressures and suctions for correlation with siITlilar data obtained during the design stage froITl boundary layer wind tunnel tests at the University of Western Ontario.

2

-2. Correlation of wind excitation with measured building vibrations and comparison with calculated building vibrations. The latter would

require access to structural design information.

3. Measurement of building displacements and strains in some of the main structural members.

It should be stressed that these objectives do not imply any concern over the design of this particular building or of the use of the boundary layer wind tunnel as a design tool. The aim is to provide much-needed field data for the further confirmation a'nd development of design procedures which are considered to be the most reliable and accurate means presently available for estimating design wind forces. Commerce Court represents an excellent opportunity for field research precisely because it will ｾ･ designed using these procedures.

II. PROPOSED INSTRUMENTATION

Instrumentation will be required for two main types of observations:

1. Measurement of Wind Excitation of the Building

(a) Wind speed and direction - preferably by an anemometer and wind vane mounted on a tower on top of the building.

(b) Wind pressures and suctions measured at exterior wall orifices on all four sides, at each of four levels.

2. Measurem,ent of Building ｒ･ｳｰｯｾｳ･ to Wind

(a) Building movement (particle velocity) in response to dynamic excitation by wind - using Willmore seismometers at three of the four levels on which pressures are measured.

(b) Strains in selected columns near the bottom, middle and top of the building, and also in a mean beam near a beam-to-column connection, using electrical resistance strain gauges.

(c) Measurement of foundation movement using a Willmore seismometer.

(d) Measurement of total building displacement by means of some line-of-sight method should be considered in addition to seismometer measurements.

Ill. EXT ERIOR WALL ORIFICES

The exterior wall openings for pressure measurements would be not more than ｾ in. in diameter, and should preferably be located in locations corre sponding to those of the wind tunnel model. The model has 192 openings, 24 on each of eight levels. For the actual building it is proposed that 12 openings be located as closely as can be arranged to corresponding locations close to the 3rd, 5th, 6th and 7th levels in the model representation (Figure 1).

Space (about 8 in. long by 4 in. in diameter) with access for installation and periodic adjustment of transducers (Figure 2) would be required at each of the locations, perhaps incorporated into under-the-window induction units. A plastic tubing

(t

in. o. d.) and a strain gauge cable (about ｾ in. o. d. ) would be used to provide a reference pre s.sure and signal connection from a central location on each level to each of the locations.

All openings would not be in use at one time since only about 24 channels of recording will be allocated to pressure transducers, but various combinations could be sampled on different occasions. Whether in use for measurements or not, the openings would be so designed as not to interfere in any way with the successful performance of the wall.

IV. VERTICAL TRUNK LINE FOR SIGNAL CABLES

The plastic tubing corning from each of 12 taps on each floor level would terminate at the central location chosen for the vertical run of signal cables (Figure 1), with a space for the recording equipment somewhere along this vertical spine. (The most economical location for the recording equipment would be the 6th tapping level, or about

70 per cent of the building height). The vertical signal cables should accommodate about 30 channels to allow flexibility in arranging

experiments, arriving from the various tapping levels, and also from strain gauges on columns near the bottOlTI of the building. Wires would also corne from the anemometer above the roof level.

A 2-in. -diameter conduit or equivalent provision should be sufficient for the installation of all vertical signal leads.

V. WILLMORE SEISMOMETERS

The seismometers are cylinders about 15 in. long by 8 in. in diameter lying in a cradle with axis horizontal. They could be installed

4

-on a shelf attached to the structural frame near the centre of the building at each of the four instrumented levels and left in place during the research project. They are fairly sensitive and should be protected against

accidental bumps or movement.

VI. ELECTRICAL RESISTANCE STRAIN GAUGES

Two columns would be chosen at each of three levels to provide six measurements of strain in the structural frame. The same sort of signal leads are used in this case as the signal leads to the pressure

transducers. An additional strain measurement on a girder near a column would be recorded during part of the research project.

VII. FOUNDATION DISPLACEMENT

Structure -foundation interaction is an important aspect of building vibration for which little field information is available; although the

building is to be founded on shale and should thus have only minimal interaction, it does represent a point on the range of possible foundation conditions. It would therefore be worthwhile to carry out some meas-urements while recording the output of a Willmore seismometer on the lowest basement floor. Signal cables would thus be needed from the bottom of the building to the central recording location. This particular

seismometer would have to be securely tied to the basement slab. In addition to wind excitation, there will undoubtedly be excitation from traffic which can be correlated with building vibration.

VIII. TOTAL BUILDING DISPLACEMENT

Equipment for measuring total displacement by a line -of - sight technique is not available at present in the Division but, if at all possible,

such measurements should be made. Various methods, such as some type of optical system, or a laser beam. with photo-cell sensors, should be investigated. This appears to be the m.ost practical way to measure the slowly varying drift of the building caused by the variation in m.agnitude and direction of the m.ean wind load. On top of this slow variation will be superim.posed the building vibrations, also of a relatively slow nature (perhaps with a period of 7 to 10 seconds).

IX. RECORDING LOCATION

The digital data acquisition system. to be em.ployed in this project now occupie s a cabinet about 3 ft square by 7 ft tall, and weighs about 600 lb. (Figure 3). Power requirem.ents are 115 volts, 60 cycle a. c. and power consum.ption is about 750 watts. Pos sibly additional equipm.ent will becom.e desirable, but this will give some idea of the present instru-mentation.

x.

GENERAL ORGANIZATION OF RESEARCH PROJECT

Planning of the field measurements should be coordinated with the design and construction phases and should be closely related to the wind tunnel model investigation. Perhaps the major difference between wind tunnel tests and field tests is that in the latter one has to wait for suitable wind conditions before each change to a new arrangement of transducers or seismometers.

The data system is de signed to operate unattended, continuously scanning the transducers while monitoring one particular channel with a voltage comparator. When the signal on that particular channel

(recording, say, wind speed) exceeds a preset voltage level, recording on magnetic tape is initiated and a complete file of data is recorded.

The recording system must be checked at least once a month, to change magnetic tapes, check zero drift and calibration of transducers, and possibly to change to a new configuration once the previous one has been adequately explored.

The whole observation period would probably extend over two to three years, although useful results may become available almost immediately. It would be necessary to arrange for access to the

transducers (at the convenience of the tenants on the instrumented floors) from time to time (but not more frequently than at average intervals of 1

i

to 2 months). This work could be done at night.

The estimated input from DBR/NRC in terms of manhours per year is 1200 hours for research engineers and 600 hours for technicians. Of these amounts, roughly half would be spent at the building during installa-tion stages, initial check-out of instruments, and regular servicing and

adjustments. The remaining time would be taken up with analysis of the records and preparation of reports. Thirty to 50 hours of computer time per year may be required in the analysis of the records.

As the project progresses, ·various short-term experiments ITlay become desirable within the framework of the instrumentation already described (subject to approval by the owners). For exaITlple, to gain a more complete picture of the building vibration, more seisITlometers ITlight be brought in temporarily and arranged on the four instrumented levels about 20 ft away from the ones already there. This would allow an estimate of torsion. In some cases, two seisITlometers might be set out, one along each of the main axes of the building to measure the relative amplitudes of vibration about the long and short axes.

As in other similar studies, the results will be used to provide information needed for a better understanding of the performance of full-scale buildings, ｰ｡ｲｴｩｾｵｬ｡ｲｬｹＬ in this case, of building response to the effects of wind loading. This information will be made available through published papers, answers to inquiries of designers and by providing technical as sistance to those engaged in revising the

National Building Code of Canada. Nothing will be published about this work, however, without the full and written agreement of all the co-operating partie s.

__ The proposed instrumentation and Itmo dus operandilt have

been outlined in some detail in order to give as faithful a picture as possible of the requests that might be made to the builders and owners during the course of the project. Of course, details remain to be worked out in consultation with those responsible for the planning and execution of the building. From the point of view of the Division one important asset of the proposed research is the opportunity offered to co-operate with the designers and the owners, not only in the planning and installing of instrumentation, but also in the later assessment and interpretation of the results in the light of the design assumptions and procedures used.

XI. CONCLUSIONS

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48 TAPS

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DIAM.) AND CABLES PROPOSED FOR WIND

PRESSURE MEASUREMENTS ON COMMERCE COURT

Figure 2

Transducer £01' rDeasuring air preSSlJrc cJjfferences aCrOfjS the

exterior wa]] of a bui]cling - shown lnountcd on a transparent pane] inserted into a \'vindO\v opening.