Cress
Help - Ice forces - A21.2
Cress
Help - Ice forces - A21.2
Period character number
Period characteristic number: see [a]:
The period characteristic number is the sum of the continuous series of daily
average temperatures during an ice period and is a measure for the severity of the frost period. An ice period is defined
as the time in which the ice can be present (between the first and latest ice accretion) and comprises both the ice growth and
the thaw periods. However the assumption usually made is that an ice period begins when the air temperature first falls below
the freezing point (t0) and ends when the temperature again rises above freezing point (tn). Thus:
with t0 and tn in hours and taking into consideration the absolute values of T.
In practice calculations are usually made with the average daily air temperature Td:
The probability that the frost period is more severe than the period with value Sg for the
Dutch situation is (lognormal distribution): The probability of one or more frost periods per winter for the Dutch situation is ca. 0.6. The ERF-function is given by:
References
equation 2
equation 3
with a = 0.922 and b = 4.034
equation 4
[a] ing. C.J.A. Zijlmans, IJsbezetting -bestrijding op de grote rivieren in Nederland, Literatuurstudie, Rijkswaterstaat, Dir. benedenrivieren, afd. AXB, org. IJsopruiming, sektie onderzoek, nov. 1980.
[b] Stormvloedkering Nieuwe Waterweg, document ontwerp, deel 1, RWS Directie sluizen en stuwen, 31 juli 1989, BMK.
[c] ir A.W. de Haas, april 1986, Ice afvoerproblematiek voor de grote rivieren en de Rijndelta, bijzondere onderwerpen, RWS dir. Benedenrivieren, Organisatie IJsopruiming Sectie Onderzoek.
[d] ir T. Stoutjesdijk e.a. Grondmechanica Delft, oktober 1991, Taludbekledingen van gezette steen, bijzondere belastingen, co-320030/3.
[e] H.R. Kivisild, Proceedings 8th IAHR-congres 1959, Montreal-Canada-Volume III, "Ice problems in hydraulic structures.
[f] ir F. Gerritsen, Proceedings POAC-conference "The first international conference on port and ocean engineering under Arctic conditions", Vol. I Norway 1971, Ice problems in Dutch rivers and estuaries, blz. 582 e.v.
[g] Korzhavin, K. N., Action of ice on engineering structures, Novosibirsk, Akad. Nauk. USSR 1962.Vertaling: TL 260 van CRREL Hanover, New Hampshire, 1971
[h] Russische ontwerpregels uit 1986.
[i] Carstens T. editor, Working group on ice forces on structures, A State-of-the-art report, special report 80-26, june 1980.