Deflection Measurement of Masonry Arch Bridges with Tall Piers: Case Study of Shahbazan Bridge

A common practice for detailed assessment of masonry bridges is to use recorded deflection signature of mid-span of such structures due to predefined loading schemes. However, measuring the deflection of bridges with tall piers or those situated over deep valleys introduces certain difficulties, since common deflection-meters require a reference point relative to which the measurement is carried out. Common approaches currently proposed by researchers include indirect measurement of deflection based on acceleration or tilt measurements. However, due to small values of deflection in masonry arch bridges, such approaches may not produce the expected results. Moreover, optical methods are difficult and rather expensive to implement due to small deflection values and far reaching points. This paper proposes the application of piers as the reference point of common deflection meters. To demonstrate the applicability of the proposed approach, a case study is carried out in which a 70 years old railway masonry arch bridge is instrumented for structural health monitoring. The studied bridge is a seven span railway masonry arch bridge with tall piers of almost 40 meters and span lengths of 21.5m. It is concluded that vertical deflection signature of conventional method could be derived from inflating that of proposed method by a factor of 1.86. Therefore, the method proves to be practical for the purpose of structural health monitoring and calibration of numerical models.