Static and Dynamic Stiffness of Reinforced Concrete Beams Strengthened with Externally Bonded CFRP Strips.

Michał Musiał,Tomasz Trapko,Jacek Grosel

doi:10.3390/ma14040910

Abstract

This paper presents experimental investigations of reinforced concrete (RC) beams flexurally strengthened with carbon fiber reinforced polymer (CFRP) strips. Seven 3300 mm × 250 mm × 150 mm beams of the same design, with the tension reinforcement ratio of 1.01%, were tested. The beams differed in the way they were strengthened: one of the beams was the reference, two beams were passively strengthened as precracked (series B-I), two beams were passively strengthened as unprecracked (series B-II) and two beams were actively strengthened as unprecracked (series B-III). Moreover, the strengthening parameters differed between the particular series. The parameters were: CFRP strip cross-sectional areas (series B-I, B-II) or prestressing forces (series B-III). The beams were statically loaded, up to the assumed force value, in the three-point bending test and deflections at midspan were registered. After unloading the beams were suspended on flexible ropes (the free-free beam system) and their eigenfrequencies were measured using operational modal analysis (OMA). The static measurements (deflections) and the dynamic measurements (eigenfrequencies) were conducted for the adopted loading steps until failure. Static stiffnesses and dynamic stiffnesses were calculated on the basis of respectively the deflections and the eigenfrequencies. The qualitative and quantitative differences between the parameters are described.

Highlights

One of the basic ways in which civil engineering structures can be diagnosed is by observing their response to external impacts of usually known magnitude
The results shown in the diagram (Figure 19) were were merely merely aa qualitative qualitative confirmation confirmation of other test results (e.g., [42]), which is presented here as a formality
Static stiffness EIS was calculated from formula (9) on the basis of the deflections

Summary

Introduction

One of the basic ways in which civil engineering structures can be diagnosed is by observing their response to external impacts of usually known magnitude. The intensive development of non-destructive structural diagnostics in recent decades [1,2] has resulted in new attractive methods of testing building structures, elements and materials. Using OMA one can determine certain dynamic parameters (e.g., eigenfrequencies, eigenforms and damping) of a structure on the basis of its response to random excitations, without measuring the parameters. This method is applicable to traditionally understood static loading modes (light wind blows, vehicle traffic close to the structure)—the metrological precision of the measuring instruments currently used guarantees acquiring vibrations caused even by such a small load. OMA is, a method that is widely used in both statically and dynamically loaded structures

Objectives

Results

Discussion

Conclusion