Monitoring high-rise building deformation using Global Positioning System

Abstract

Deformation of engineering structures is often measured in order to ensure that the structure is exhibiting a safe deformation behaviour. For example, the deformation of high-rise building can be monitored by using geodetic method such as Global Positioning System (GPS). This paper discusses the monitoring of high-rise building using the GPS methods. The case study is the KOMTAR building, in Penang, Malaysia. Six control points have been established whereby four of them is located on top of the building itself, and the other two is located at the KOMTAR Plaza compounds.. The field measurements have been carried out in two different epochs, October 2000 and February 2001. The GPS observation and deformation data have been processed and analysed by using the SKI TM and GPSAD2000 softwares, respectively. The results showed that there is no movement occurred in the building.

Introduction

Engineering structures (such as dams, bridges, high rise buildings, etc.) are subject to deformation due to factors such as changes of ground water level, tidal phenomena, tectonic phenomena, etc. Cost is more than offset by savings and by improvements in safety both during and after constructions. As a result, the design, execution and analysis of such surveys are a matter of considerable practical importance. Expanded resource development, the trend towards potentially-deformation-sensitivity engineering and construction projects, and growing geosciencetific interest in the study of crustal movement have all combined to increase awareness of the need for a comprehensive integrated approach to the design and analysis of such deformation surveys. Deformation refers to the changes of a deformable body (natural or man-made objects) undergoes in its shapes, dimension and position. Therefore it is important to measure this movements for the purpose of safety assessment and as well as preventing any disaster in the future.

Deformation measurement techniques generally can be divided into geotechnical, structural and geodetic methods (Teskey and Poster, 1988). The geodetic methods (highly understood by land surveyors) that can be used are Global Positioning System (GPS), close range photogrammetry, total station (terrestrial survey), very long baseline interferometry and satellite laser ranging. The survey methods can be further subdivided into the survey network method and direct measurement methods. In geodetic method there are two types of geodetic networks, namely the reference (absolute) and relative network (Chrzanowski et. al., 1986).

The selection of most appropriate technique or combination of techniques for any particular application will depend upon cost, the accuracy required, and the scale of the survey involves. Therefore several aspects related to the optimal design of the networks, measurement and analysis techniques suited to the monitoring surveys have to be considered. The design of monitoring scheme should satisfy not only the best geometrical strength of the network but should primarily fulfill the needs of subsequent physical interpretation of the monitoring results. Selection of monitoring techniques depends heavily on the type, the magnitude and the rate of the deformation. Therefore, the proposed measuring scheme should be based on the best possible combination of all available measuring instrumentation. A common feature for both geodetic and satellite methods in monitoring scheme involves the following three stages:

The development of a network configuration,

The execution process that runs a designed network into reality which deals with both the documentation of the proposed network stations and the actual field measurement techniques, and

The network analysis that deals with the processing and analysis of the collected geodetic data.

GPS Background and Structural High Rise Building

GPS is satellite based positioning system, which has been developed by the US Department of Defense (DoD) for real time navigation since the end of the 70’s. It has made a strong impact on the geodetic world. The main goal of the GPS is to provide worldwide, all weather, continuous radio navigation support to users to determine position, velocity and time throughout the world. It consists of three segments: the space, control and user segment. The GPS can be used for absolute and relative geodetic point positioning. Its primary task is to measure distances between 24 satellites in known orbits about 20,000 km above the earth and provide the user with the information of determining user’s position, expressed in the geocentric 3D coordinate system (WGS84).

GPS techniques have several advantages as a monitoring tool. The surprisingly high accuracies of relative GPS measurements are finding an application in monitoring surveys in areas where stations require intervisibility and weather conditions. Currently, with the deployment of the full satellite constellation, continuous and automated monitoring using GPS will become increasingly practical and cost-effective. Thus, the potentials of GPS as a super positioning tools brought a fresh air to the field of monitoring surveys, especially in areas where quick results could save lives and property. In principle, the monitoring of high-rise building using GPS can be performed episodically (epoch intervals) or continuously. Current GPS accuracy estimates range from 1–2 ppm for regional baseline vectors determined using commercial production software (DeLoach, 1989).

High-rise building is defines as a multistory building tall enough to require the use of a system of mechanical vertical transportation such as elevators. Although originally designed for commercial purposes, many high-rise buildings are now planned for multiple uses. They arose in urban areas where increased land prices and great population densities created a demand for buildings that rose vertically rather than spread horizontally, thus occupying less precious land area. The foundation of high-rise buildings must support very heavy gravity loads and they usually consist of concrete piers, piles or caissons that are sunk into the ground. The most important factor in the design of high-rise buildings is the building’s need to withstand the lateral forces imposed by winds and potential and ground movements. Most high-rise buildings have frames made of high strength steel and concrete. Their frames are constructed of columns (vertical-support members) and beams (horizontal-support members). Cross bracing or shear walls may be used to provide structural frame with greater lateral rigidity in order to withstand wind stress. Even more stable frames use closely spaced columns at the building’s perimeter, or they use the bundled-tube system, in which a number of framing tubes are bundled together to form exceptionally rigid columns. Curtain walls enclose high-rise buildings; these are non-load-bearing sheets of glass, masonry, stone or metal that is affixed to the building’s frame through a series of vertical and horizontal members called mullions and muntins.