CHAPTER 5.1: WAVE IMPACT LOADS - PRESSURES AND FORCES

1 - 1 - CHAPTER : WAVE IMPACT LOADS - PRESSURES AND FORCES -A. KORTENHAUS1); H. OUMERACI1); ALLSOP2); MCCONNELL2); VAN GELDER3); HEWSON4); ); G. M LLER5);M. CALABRESE6); D. VICINANZA6) 1) Leichtwei -Institut, Technical University of Braunschweig, Beethovenstr. 51a, DE-38106 Braunschweig, Germany2) HR Wallingford, Howbery Park, GB-Wallingford OX10 8BA, ) Delft University of Technology, Faculty of Civil Engineering, Stevinweg 1, NL-2628 CNDelft, The Netherlands4) University of Plymouth, School of Civil and Structural Engineering, Palace Street, GB-Ply-mouth PL1 2DE, ) Queens University of Belfast, Department of Civil Engineering, Stranmills Road, GB-Bel-fast BT7 1NN, Northern Ireland6) Universit degli Studi di Napoli 'Frederico II', Dipartimento di Idraulica, Via Claudio n.

2 21,IT-80125 Naples, ItalyABSTRACTThe tentative procedures for both IMPACT and uplift loading proposed by Oumeraci andKortenhaus (1997) have been brought together and amended by many partners in PROV-ERBS. This paper proposes a procedure to calculate time-dependent PRESSURES , FORCES and le-ver arms of the FORCES on the front face and the bottom of a vertical breakwater. For this pur-pose, (i) the data sets on which this method is based are briefly described or referred to; and(ii) a stepwise procedure is introduced to calculate the wave loading supported by some back-ground and data information. Suggestions for estimating the FORCES on a caisson in feasibilitystudies are also / HR / DUT / UE / UoN / UoP / QUBA. KORTENHAUS ET 2 impacts on vertical breakwaters are among the most severe and dangerous LOADS thistype of structure can suffer.

3 Whilst many design procedures for these structures are well estab-lished worldwide recent research in Europe has shown that some of those design methods arelimited in their application and may over- or underpredict the loading under important condi-tions. This will then lead to overdesigned and very expensive structures or, even more danger-ous, to underdesign and consequently to danger to personnel and PROVERBS engineering experience from various fields (hydrodynamic, foundation,structural aspects) concerned with vertical breakwaters has been brought together. Further-more, data available from different hyraulic model tests, field surveys and experience fromnumerical modelling were collected and analysed to overcome the aforementioned from both universities and companies were working together to derive new meth-ods for calculating FORCES and PRESSURES under severe IMPACT conditions taking into accountthe influence of salt water and aeration of the water.

4 This new approach was then furtheroptimized by taking into account the dynamic properties of the structure itself and the founda-tion of the breakwater (see Volume I, CHAPTER ). The multidirectionality of the waves ap-proaching the structure (Vol. I, CHAPTER ) has also been intention of this paper is to describe a procedure to calculate both IMPACT and uplift load-ings under 2D conditions and to give references to more detailed work on the different aspectsof the steps described in here. For sake of completeness and easier understanding of the wholemethod some parts had to be repeated from other sections within Vol. II of the PROVERBS report. This was considered to be more useful rather than giving too many references to dimensions and a sketch of a typical caisson breakwater are given in Fig.

5 IMPACT LOADS : FORCES AND PRESSURES - 3 -Tab. 1: Overview of design methods for wave OF RECENT WORKT here are a number of formulae available for different types of waves breaking at the struc-ture. These formulae generally include magnitudes of maximum PRESSURES , their distributionsand FORCES . In some cases, uplift PRESSURES are given as well. All formulae are fully empiricalor semi-empirical as the process of wave breaking at the structure is still not fully 1 summarizes the most important methods in a chronological order, details are given inthe respective WavesSainflou1928yesyes, butdifficultnovertical wall, no bermMiche-Rundgren19441958yesyesnodesign curves from SPM, 1984 Goda1985yesyesyesmost-widely used designmethodImpact WavesHiroi1919yesyesnovertical wallBagnold1939---conceptual model onlyMinikin1963yesyesnosometimes incorrect dimen-sions!

6 Ito1971yesyesyesBlackmore &Hewson1984yesyesnoPartenscky1988yesnot givennoair content of wave neededKirkg z19901995yesyesnovertical wall onlyTakahashi1994yesyesyesextension of Goda modelAllsop et et of FORCES and rise timeOumeraci &Kortenhaus1997yesyesyestime-dependent approach!LWI / HR / DUT / UE / UoN / UoP / QUBA. KORTENHAUS ET 4 -McConnell1998noyesnoamendment of O&K, 1997 Hull & M ller1998yesyesnoamendment of O&K, 1997 Vicinanza1998yesyesnoamendment of O&K, 1997 Broken WavesSPM1984yesyesnovertical walls onlyCamfield1991yesyesnoamendment of SPM, 1984 Jensen1984yesyesyesCrown wallsBradbury &Allsop1988yesyesyesCrown wallsPedersen1997yesyesyesCrown wallsMart n et wallsThis paper is concentrated on calculation of pressure distribution and related FORCES underimpact conditions.

7 Furthermore, the dynamic characteristics of IMPACT FORCES were consideredessential for the behaviour of the structure subject to this type of loading. The designprocedure is therefore based on the approach by Oumeraci and Kortenhaus, 1997 which wasderived from solitary wave theory but amendments were made to many details like thestatistical distributions of IMPACT and uplift PRESSURES , the vertical pressure distribution at thefront face, and the relation between rise time and duration of IMPACT FORCES . OF DATA SETSD ifferent hydraulic model tests have been carried out and analysed to obtain the designmethod proposed in this paper. These tests are summarized in Tab. 2 where the mostimportant information is given.

8 Furthermore, references are added where more detailedinformation on these tests is IMPACT LOADS : FORCES AND PRESSURES - 5 -Tab. 2: Overview of hydraulic model tests (random waves) )Scalefsam[Hz] ) )ReferencesWKS199311:15600901:50121106 Oumeraci etal., 1995 GWK1993/9411:51001001:5062105 McConnell& Korten-haus, 1996HR941994101:204005001:5021784 PIV199411:5040011:20777-Oumeraci etal., 1995HR97199711:20100010001:501:201:101:7 9-McConnell& Allsop,1998 QUB199731:3010008001:501214 Kortenhaus& L ffler,19981) number of configurations tested; 2) number of transducersIt may be assumed from the differences in the number of waves per test and the acquisitionrate that results of pressure distributions and FORCES might also differ , data analysis has confirmed that most of the data sets fit well to each otherwhich will be explained in more details in the successive STEPSLWI / HR / DUT / UE / UoN / UoP / QUBA.

9 KORTENHAUS ET 6 - IMPACT load(Goda-formula not applicable)(Goda-formula applicable)"Pulsating load"t/Tt/Tt/T(a) Standing wave(b) Slightly Breaking wave(c) Plunging breakerFD g periodFig. 1: Pulsating and IMPACT load - problem of wave IMPACT loadingA simple method is needed to distinguish between:(b)quasi-standing LOADS for which available formulae ( Goda, see Vol. I, Chap-ter ) without any account for load duration can be used (Fig. 2a);(d)slightly breaking wave LOADS which already consist of some breaking waves but notsignificantly exceeding the Goda LOADS (Fig. 2b);(f)an IMPACT load for which new formulae including IMPACT duration are to be used(Fig. 2c); and(h)broken wave LOADS , the waves already broke before reaching the this purpose the PROVERBS parameter map (Fig.)

10 3) was developed which is in moredetail described in CHAPTER of Volume IIa. Input for this map are geometric and waveparameters which in combination yield an indication of a certain probability that one of theaforementioned breaker types will IMPACT LOADS : FORCES AND PRESSURES - 7 -"Vertical"Breakwaterh < * < h < *Crown WallsRubble mound Breakwaterh > *Low < h < *High < h < *Large < H < *Small < H < *Large < H < *Small < H < *Narrow < B < *Moderate berm < B < *Wide bermB > *dhsSWLSWL withSmall waves H < *Large < H s*F =FhhD g H2b*hb*hbsh =s*hsHsH =*LBeqB =;;; * * *Slightly breaking waveImpact loadsBroken waveFig. 2:PROVERBS parameter @1&Cr1%Cr(1)Lpi'L0@ height at the structureA breaking criterion which accounts for the reflection properties of the structure has been sug-gested by Calabrese (1997) (see CHAPTER of Volume IIa) based on extensive random wavetests in hydraulic model tests and previous theoretical works (Oumeraci et al.