Technical Paper by J.H. Greenwood - IGS - International ...

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GREENWOOD D Designing to Residual Strength Instead of Stress-Rupture f m12 = partial factors for the uncertainty in extrapolation (dimensionless) f m21 = partial factor for installation damage (dimensionless) f m22 = partial factor for environmental effects (e.g. ultraviolet light, hydrolysis of polyester and oxidation of polyolefins) (dimensionless) K = stress concentration factor = σYa ½ for simple geometries (Pa m ½ ) K IC = initial critical stress concentration factor (Pa m ½ ) n = index value (dimensionless) T = applied load (N/m) T CR = unfactored design strength (N/m) T D = geosynthetic reinforcement design strength (N/m) T R = residual (or available) geosynthetic strength (N/m) t = time (s) t d = design life (s) t f = time to failure (s) Y = geometrical factor (dimensionless) σ = applied stress (N/m 2 ) σ 0 = initial strength (N/m 2 ) σ t = residual strength (N/m 2 ) 10 GEOSYNTHETICS INTERNATIONAL S 1997, VOL. 4, NO. 1
Discussion and Closure DESIGNING TO RESIDUAL STRENGTH OF GEOSYNTHETICS INSTEAD OF STRESS-RUPTURE TECHNICAL NOTE UNDER DISCUSSION: Greenwood, J.H., 1997, “Designing to Residual Strength of Geosynthetics Instead of Stress-Rupture”, Geosynthetics International, Vol. 4, No. 1, pp. 1-10. DISCUSSER: S-C.R. Lo, Senior Lecturer, School of Civil Engineering, University College, University of New South Wales, Canberra, Australia, Telephone: 1/61-6-2688349, Telefax: 1/61-6-2688337, E-mail: srl@octarine.cc.adfa.oz.au. PUBLICATION: Geosynthetics International is published by the Industrial Fabrics Association International, 1801 County Road B West, Roseville, Minnesota 55113-4061, USA, Telephone: 1/612-222-2508, Telefax: 1/612-631-9334. Geosynthetics International is registered under ISSN 1072-6349. REFERENCES OF DISCUSSION AND CLOSURE: Lo, S-C.R., 1997, “Discussion of ‘Designing to Residual Strength of Geosynthetics Instead of Stress-Rupture’ by Greenwood, J.H.”, Geosynthetics International, Vol. 4, No. 6, pp. 673-675. Greenwood, J.H., 1997, “Closure of Discussion of ‘Designing to Residual Strength of Geosynthetics Instead of Stress-Rupture’”, Geosynthetics International, Vol. 4, No. 6, pp. 675-677. Discussion by S-C.R. Lo The author of the paper has presented a more rational and less conservative method for assessing the load carrying capacity of geosynthetics under long term loading. However, clarifications are needed to ensure the proposed method is applied in a way compatible with the design conditions and philosophy of the design code used. The latter cannot be over-emphasised because of the introduction of limit state design codes that use a series of somewhat confusing partial factors. In a limit state design code, partial factors are used in lieu of a single factor of safety. The design strength, T D , is obtained by applying a partial factor f m to T CR , the rupture strength at the specified design life obtained by extrapolation of test data. In the context of limit state design, f m is used to cover uncertainties in the determination of T CR and the loss in effective load carrying area (say, due to construction damage). In BS 8006 (1995), f m is considered as the product of a number of partial factors f m11 , f m12 ,etc.in GEOSYNTHETICS INTERNATIONAL S 1997, VOL. 4, NO. 6 673
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