1、毕业设计 外文翻译 1 外文原文 1 Increased Snow Loads and Wind Actions on Existing Buildings: Reliability of the Norwegian Building Stock Vivian Meloysund, Ph.D. ； Kim Robert Liso, Ph.D. ； Jan Siem ； and Kristoffer Apeland Abstract: Results from an investigation of snow loads and wind actions on 20 existing build
2、ings in Norway are presented. The objective has been to investigate to what extent existing buildings meet current regulatory requirements relating to safety against collapse owing to snow loads or wind actions. Eighteen buildings have a utilization ratio of more than 1.0 under current regulations.
3、The new design rules have led to most of the buildings investigated having reduced safety against collapse owing to snow and greater safety against collapse owing to wind actions than the regulations now demand. The investigation indicates too low reliability for a considerable number of buildings a
4、ccording to current building regulations when evaluating the possible consequences of the conclusions in a national perspective. Scenarios for future climate change indicate both increased winter precipitation and increased temperatures, and thus changing the snow loads on roofs. Wind scenarios for
5、the decades to come indicate an increase in frequencies of strong winds in areas also exposed today. Thus, the future reliability of the buildings in these areas could decrease. CE Database subject headings: Bearing capacity； Buildings； Climatic changes； Norway； Reliability； Snow loads； Structural d
6、esign； Structural safety； Wind loads. Introduction Background Large snow loads on during the winter of 1999/2000 led to the collapse of several buildings in northern Norway. The accident at Bardufoss Community Centre, where the roof caved in and claimed three lives, was the most serious of these acc
7、idents (Fig.1). The most important causes of this collapse were a faulty construction of the roof when the building was erected and larger snow loads on the roof than it was designed for. 毕业设计 外文翻译 2 Principal Objectives and Delimitations The principal objective of the investigation has been to obta
8、in a reliable indicator as to whether existing buildings in Norway meet current regulatory requirements concerning safety against collapse owing to snow loads and/or wind actions, and also to establish a basis for the analysis of future climate change impacts on the Norwegian building stock. The ana
9、lysis encompasses design documentation investigations and field studies of 20 existing buildings in five high-snowfall and five high-wind municipalities in Norway (Siem et al. 2003； Meloysund et al.2004). Statistical data for building types, year of construction, and geographical localization of the
10、 approximately 3.7 million registered buildings in Norway are available in the Ground Property, Address and Building Register (GAB). Special attention has been paid to exposed types of buildings, and the buildings have been randomly selected within the exposed building categories. Assessments of whe
11、ther the regulations are satisfactory and theoretical parameter studies of the regulations are not included in the investigation. The investigation focuses on assessing the buildings main load-bearing structures and, to a lesser extent, their secondary load-bearing structures. Building Regulations a
12、nd Design Codes Development of Design Codes for Snow Loads and Wind Actions The building regulations of December 15, 1949 referred to a general snow load on roofs 毕业设计 外文翻译 3 corresponding to 1.5KN/m2 . This value could be reduced or increased by the individual building authority with the Ministrys
13、approval. The importance of the shape of the roof for the size of the snow load on the roof was calculated in a simple way. Structures should normally be designed for a wind pressure equal to 1.0 KN/m2 , while a wind pressure equal to 1.5 KN/m2 should be used in exposed areas. In heavily exposed are
14、as, building authorities could increase these basic values with the Ministrys approval. The sum of the wind shape factors for lee and windward walls for a closed building was 1.2. In NS 3052 (Standard Norway 1970) snow maps were introduced showing zones with roof snow loads values of up to 1.5 KN/m2
15、 , between 1.5 KN/m2 and 2.5 KN/m2 , and above 2.5 KN/m2 . Four curves for the wind pressure were introduced: Curves A, B, C, and D, as seen in Fig.2. The code quoted many more-detailed rules for the wind shape factors for the lee and windward walls was in the code also set to 1.2. Compared to the b
16、uilding regulations of 1949, the changes in NS 3052 largely implied a reduction in the wind velocity pressures in exposed areas. In NS 3052 the partial factor method was introduced. The partial factor for snow loads was set to 1.6 while the partial factor for wind actions was set to 1.5. In NS 3497-
17、4 (Standards Norway 2002a), a classification of the whole country has been carried out so that wind exposure for all 434 municipalities is defined. Exposure is defined by means of a reference wind velocity (varies between 22 m/s and 31 m/s). Roughness of the terrain in an area 10 km against the wind
18、 direction is important for the wind pressure (in the code called the gust velocity pressure). The code defines five such categories of terrain roughness. Other parameters of importance for the gust velocity pressure are the wind direction, the height of the building site above sea level, and the to
19、pography. In this regulation amendment process, NS 3490 (standards Norway 1999) prescribes a 50-year return period for environmental loads. The partial factors for environmental loads are set to 1.5. A reduction factor kL by which the partial factor must be multiplied is introduced. The extensive re
20、visions of the codes have increased the level of detail in the regulations considerably. The objective is to achieve a safety level in accordance with Table 2. In other words, the intention is to achieve a more uniform safety level for buildings that have the same reliability class even if they are built in different places, and also to obtain different safety levels for structures classified in different reliability classes. A thorough description of the historical development of design loads for wind actions and snow loads is presented by Meloysund et al.(2004).
