Comparison of Anchorage Systems for Externally Bonded FRP Laminates

This paper reports the results of an experimental program to investigate the bonding behaviour of two different types of anchorage systems for externally bonded FRP laminates for strengthening one way RC slab, mechanicaland fiber anchorage system. The overall experimental program consisted of seven flexure tests on RC slab specimens strengthened with a mechanical anchorage system and another seven flexure tests on RC slab specimens strengthened with a fiber anchorage system. The influence of different types of anchorage systems, numbers of anchors and anchor spacing are studied in this paper to evaluate the behaviour of strengthened one-way slabs. The performance of each anchorage system is presented, discussed, and compared in terms of deflection, debonding mode, and failure mode. General from the experimental results, it is found the anchorage system significantly reduces the slab deflections and increases the slab strength and slip capacity, in comparison with unanchored control slabs. The findings indicate that the mechanical technique could represent a better alternative to the fiber anchorage technique because it allows debonding to be more delayed, and hence FRP tensile strength to be better exploited.


A. Materials
The 28-day compressive strength of concrete is 30 MPa. The steel reinforcement is Grade 360 with nominal yield and ultimate strength of 360 and 520 MPa, respectively. The CFRP strip is Sika S1012. Sika CarboDur S1012 has an elasticity modulus of 165,000MPa, a rupture tensile strength of 3100 MPa and an ultimate elongation of 1.5%. Sika 30 epoxy is used for bonding. As provided by the manufacture, its tensile strength at 7 days is 24 MPa. Steel and fiber anchors are shown in Fig. 1, 2 respectively. The steel wedge bolts are singlepiece with diameter 12 mm, heavy duty anchors that are driven into pre-drilled holes. Driving of the wedge bolt can be performed with a common rotary drill.

B. Test Specimen
The test specimen is 2000 mm long, 400 mm wide and 120 mm deep. Each slab is singly reinforced at tension side by 412 with a clear cover 20 mm as shown in Fig.3. For the strengthened slabs, one CFRP strip with 1750mm length, 50mm width and 1.2mm thickness is bonded to the tension face of the slab. Sika 30 epoxy is used for bonding. The Properties of CFRP composites are given in Table I.

C. Test Matrix
The test matrix is given in Table 2. A total of fourteen slabs are used in this study. Two slabs(S-01and S-02) are used as control specimens while the other twelve slabs are strengthened with CFRP strip. Two slabs (S-03 and S-04) are without strengthened anchors. Slabs (S-05, S-06, S-07, S-08 and S-09) had fiber anchors and slabs (S-10, S-11, S-12, S-13and S-14) had steel anchors. Slabs (S-05 and S-10) had two anchors, one anchor at each end, as shown in Figs 6 and 7 respectively, while slabs (S-06, S-07, S-08, S-011, S-12, and S-13) have fouranchors, two anchors at each end with different anchor spacing 100, 150, and 200 mm as indicated in Table  II.Slabs (S-09 and S-14) had six anchors, three at each end with anchor spacing 200 mm. All specimens' details are shown in Fig.4.

D. Test Set-up and Instrumentation
A very rigid steel frame consisting of horizontal and vertical I-sections was used as a base to support slab specimens. The tests were carried out in the reinforced concrete laboratory of the Faculty of Engineering, El-Mataria, Helwan University. The slab specimens were mounted in a horizontal position inside the steel frame to serve as a simple line support along the two edges of the slabs. All slabs are tested with an effective span of 1800 mm and a shear span of 600 mm. load is applied monotonically at the mid-span of the slab using a hydraulic actuator having a capacity of 200 kN. A spreader beam is used to transfer the load to the slab through two loading points placed at the ends of the middle third of the slab span as shown in Fig 5.One (LVDT) is placed under the mid-point of the slab to measure the deflection while a load cell is used to record the load. One strain gauge is bonded to the surface of the CFRP strip, at the mid-span. Similarly one strain gauge is bonded to the steel reinforcement bar, at the mid-span.The development of cracks and deflection were observed during loading and recorded after each increment till failure.

C. Effect of Fiber Anchorage Type, Numberand Spacing
The tested slab with two, four with spacing 100 mm and six fiber anchors is increased by 30%, 40% and 45% in strength respectively over the average capacity of the control slabs as shown in Fig.11. The debonding load for the previous slabs is increased by 5%, 13% and 17% respectively compared to the strengthened slab without anchors as shown in Fig. 12. The strength of the tested slab with two, four with spacing 100 mm and six steel anchors is increased by 50%, 75% and 88% respectively average capacity of the control slabs as shown in Fig.11. The debonding load for the previous slabs with steel anchors is increased by 21%, 41% and 51% respectively compared to the strengthened slab (S-03and S-04) as shown in Fig. 12. Although the ductility is reduced in the slabs with FRP reinforcement, the debonding ductility ratio of the slabs with steel anchors is increased over the slabs with fiber anchors. The steel anchors are effective in delaying debonding of the FRP strip by slowing the propagation of debonding cracking. The anchors are provided anchorage along the bonded length that led to a profound improvement of the bond behaviour, particularly for the full anchorage FRP bonded strengthened slabs