___

• cl HCL, pH 2.6 %7
• cl HCL, pH 2.3 %13
• 8kg NaOH, pH 14 %14
• The 9.8 MPa mean ultimate strength of the aged sample set; unexposed to corrosive agents
• (the "normal" set), was lower than its early ultimate strength value of 12.1 MPa shown in
• Figure 3 earlier. This is an expected behavior since it is determined that, the glass fiber
• reinforced material loses strength and ductility with time [8, 9]. The elastic strength limit is
• determined to increase with time and converge to the decreasing ultimate strength value.
• DESIGN, TESTING ANALYSIS AND FABRICATION OF THE CABLE DUCT Following the determination of the design load and the mechanical properties of the
• material, the duct design and analysis commenced. The duct design enabled elastic behavior
• under service loads and ductile failure under ultimate loads. The limited number of samples
• used for this study was not large enough to define statistically the characteristic bending
• strength value. Therefore, the design used the mean of the available bending strength results. Supplemented by the findings of the previous section, the possible effects of extreme
• contamination was judged to reduce the aged bending strength of the glass fiber reinforced
• material section; which was determined to be on average 9.8 MPa, by 15%. The design
• guidelines [8, 9] frequently use and specify the material factors based on un-aged material
• properties, which for the case presented herein was 12.1 MPa. Practical Design Guide for Design with GFRC by GRCA [8] addresses the load factor as
• 4 for dead load and 1.6 for live loads. Based on the Recommended Practice for Design with
• GFRC by PCI [9], the recommendation for the dead load factor is 1.4 and the live load factor
• is 1.7. Both guides recommend the material factor for un-aged materials as 0.25. Based on the
• findings about corrosion, an additional factor of 0,85 is accounted for the 15% bending
• strength loss. 5.1 Design Figure 1 shows the design loading case for the cable duct. The design considered the
• bending effect of the lateral load applied to the sidewall at a height of 7.5 cm from the base of
• the wall. With the known elastic and ultimate stress levels, the design outcome was the base
• and sidewall thickness (t) of the duct. The lateral service load (Fs) determined earlier was 70 kgf/m.
• For the design of the cable duct, the design ultimate load (Fud): = 1.7 * = 1.7 * 70 = 119 (2)
• The design moment (Md): = * 7.5 = 893 - (3)
• The design material ultimate strength (fud): = 0.25 * 0.85 * = 0.3 * 12 = 2.5 = 25.5 2 (4)
• The material elastic strength (fe): = 10 = 102 2 (5)
• Elastic section modulus (S) relates to the length (l) and the sidewall thickness (t) of the duct: = 1. / 2 6 (6)
• Plastic section modulus (Z) relates to the length (l) and the sidewall thickness (t) of the duct: = 1. / 2 4 (7)
• Design thickness for 100 cm long cable duct: = * 893 = 25.5 * 100 * 2 4 (8)
• Stress at service load relates to the generated moment (Ms) under the service loads: = * (9) = 70 * 7.5 = * 100 * 1.22 6 2
• Figure 11 shows the cross section of the cable duct with a design base thickness of 1.2 cm and
• an average sidewall thickness of 1.2 cm. 1-meter long cable duct and duct cap consumed approximately 0.011 m3 of glass fibre
• reinforced material. The density of the glass fiber reinforced material was 2.223 kg/m3. The
• weight of 1-meter long cable duct and duct cap was 25 kgf. This was a significant saving in
• weight, compared to the weight of an ordinary 5 cm thick reinforced concrete cable duct, which was 150 kgf.
• Figure 11. Cross sectional dimensions of the cable duct and its cap in millimeters. 5.2 Analysis
• The initial design of the duct involved the application of the lateral soil pressure due to the
• vertical load as shown in Figure 1. The design of the cable duct considered the maximum
• bending stress level that occurred along the sidewalls of the duct under the effect of lateral
• soil pressure. Another design assessment included the application of the vertical design load
• acting directly on the duct through the duct cap. The assessment considered the effect caused
• by a maintenance worker walking along the top of an improperly supported duct. Continuous
• soil support should exist below the duct under sound design guidelines and installation procedures. However, the behavior assessment of the duct under the design vertical load considered an
• adverse soil support condition that considered a case without full soil support. A common
• finite element linear-elastic analysis program analyzed the behavior of the duct as a structural
• element, simply supported at its ends under the application of 200 kgf per meter vertical
• design load applied at the middle of the 1-meter span distributed along a length of 15 cm and
• a lateral design load of 70 kgf per meter distributed at mid-height along the side of the both
• walls. The analysis disregarded the beneficial effects of the cable-duct-cap for lateral support
• on the sidewalls due to friction. Figure 12 shows the loaded design model generated by 8
• node linear elastic solid elements and the bending stresses along the length of the cable duct
• under the simultaneous action of the design vertical and lateral loads.
• Figure 12. Finite element model of the loaded cable duct and bending stress distribution.
• The analysis yielded bending stresses with the highest value of 56 kg/cm 2
• compression and the highest value of 35 kg/cm2 (3.4 MPa) in tension. The analysis did not
• indicate local buckling along the compressive edges throughout the numerical evaluation. 5.3 Testing Testing sequence required production of an initial set of count-10 sets of sample cable
• ducts. The design dimensions of the cable ducts are 100 cm length, 1.2 cm average
• thickness, 16.2 cm external depth and 28 cm width. The cap thickness is 1.2 cm and the
• cap external width is 30 cm. Due to the unavailability of more elaborate high precision automated mechanical testing
• possibilities at the time of the study, manually placed precise concrete counterweight blocks
• loaded the test samples. Figure 13 shows count-four blocks weighing 20 kgf each, placed at
• the tip of the side of the cable duct. The four tested samples responded elastically to the
• loading effect of the counterweights that weighed 80 kgf.
• Figure 13. 100cm long cable duct laterally loaded with 80 kgf.
• The duct is also loaded as a simply supported beam with 225 kgf applied at the mid-span
• as shown in the right hand side of Figure 10. The simply supported condition meant to
• disregard the soil support underneath that a buried duct would normally have. The weight of
• the lower three blocks applied was 30 kgf each, the middle three was 25 kgf each and the top
• three was 20 kgf each. The 4-samples tested under vertical load did not fail. The tests did not
• reveal any signs of local buckling along the sidewall edges subjected to compression.
• 4 Fabrication An important benefit of the thin plate structure of the glass fiber reinforced cable duct is
• the possibility to cast surfaces in three dimensions [10, 11]. Figure 14 shows glass fibre
• reinforced duct samples produced by white-cement. A tongue and groove detail allowed a
• simple but an effective inter-alignment mechanism between the consecutive cable ducts.
• However, ordinary free-flow casting method employed in the production of the initial samples
• could not achieve the proposed detail unless the use of time-consuming special attachment
• installation within the mould. The out-of-plane character of the detail required the use of
• injection moulding typically employed in the plastic industry.
• Figure 14. Tongue and groove detail of the cable duct.
• A patented injection molding sequence enabled the production of the thin ducts with the
• proposed connection detail. The sequence did not require any special detailed mould
• attachments and the simple two-piece mould received mortar injection at a 0.5 bar pressure.
• CONCLUSIONS The study showed that glass fiber reinforced mortar had a potential to replace the
• normal strength reinforced concrete 5 cm thick cable ducts selected for the Ankara -
• Konya High Speed Railway shown in Figure 15.
• Figure 15. Reinforced concrete cable duct (Cap not shown).
• The material cost of the 1.2 cm thick glass fiber reinforced cable ducts was equal to the
• cm thick reinforced C30 grade concrete cable duct. Moreover, the 25 kgf/m weight of
• the proposed duct was 17% of the weight of the reinforced concrete ducts that weighed
• kgf/m. Figure 16 shows the dimensional comparison of glass fiber reinforced cable
• duct and ordinary steel reinforced concrete cable duct cross sections.
• Figure 16. Comparison of the glass fiber reinforced cable duct with the ordinary reinforced concrete duct.
• The presented study yielded the following conclusions and recommendations:
• GFRC: Recommended Practice for Glass Fiber Reinforced Concrete Panels.
• MNL-128. 4th ed. Chicago, IL: PCI. ÖZGEÇMİŞ / CV
• Niyazi Özgür BEZGİN; Yrd. Doç. Dr. (Assistant Professor)