桥梁毕业设计外文翻译--对木桥的负载和阻力系数的校准-桥梁设计(编辑修改稿)

桥梁毕业设计外文翻译--对木桥的负载和阻力系数的校准-桥梁设计(编辑修改稿)内容摘要：

es. Load and resistance parameters are treated as random variables, and therefore, the structural performance is measured in terms of the reliability index. The statistical parameters of dead load and live
traffic
load, are based on the results of previous studies. Material resistance is taken from the available test data, which includes consideration of the postelastic response. The resistance of ponents and structural systems is based on the available experimental data and finite element analysis results. Statistical parameters of resistance are puted for deck and girder subsystems as well as individual ponents. The reliability analysis was performed for wood bridges designed according to the AASHTO Standard Specifications and a significant variation in reliability indices was observed. The remended load and resistance factors are provided that result in consistent levels of reliability at the target levels. DOI: （ ASCE） 10840702（ 2020） 10:6（ 636） CE Database subject headings: Bridges, wooden。 Calibration。 Load and Resistance Factor。 Design。 Bridge decks. Structural Types Considered The calibration work is performed for selected representative types of wood bridges. In particular, simple span, twolane, nonskewed bridges with wooden ponents of short to medium spans, from 4 to 25 m （ from 13 to 80 ft） , are considered. In general, there are two types of wood bridges: structures that span by beams （ stringers or girders） or structures that span by a deck. Stringer bridges made of sawn lumber are typically short,spanning to a maximum of 河北联合大学轻工学院毕业翻译部分 17 about 8 m (25 ft). Readily available sawn lumber stringers are usually from 100 to 150 mm (from 4 to 6 in.) wide and from 300 to 400 mm (from 12 to 16 in.) deep, and these sizes often limit spacing to no more than 400–600 mm (16–24 in.) on center. However, the use of greater widths such as 20 mm (8 in.) and larger depths may allow stringer spacing to be increased, until ultimately limited by deck capacity. Stringers of glulam can be manufactured with much greater depths and widths, and can thus span much greater distances and allow wider beam spacing. Spans from 6 to 24 m (from 20 to 80 ft) are mon. The stringers support various wood deck types, which may be gluedlaminated (glulam), naillaminated (naillam),spikelaminated (spikelam), plank (4 6 in., 4 8 in.,4 10 in., and 4 12 in.), stresslaminated (stresslam), and reinforced concrete (nonposite). Laminated decks are made of vertical laminations, typically 50 mm (2 in.) thick and l00–300 mm (4–12 in.) deep, which are joined together by nails, glue,spikes, or transversely prestressed. The latter method is typically used for deck rather than stringer bridges, however. Laminations are made into panels that are usually from 900 to 1,500 mm (from 3 to 5 ft) wide. The designer may specify that these panels either be interconnected or noninterconnected (in a direction parallel to the laminations). Interconnected panels may be secured together by spikes, metal dowels, or stiffener beams, to form a continuous deck surface, whereas noninterconnected panels are left independent of one another, although in some cases the Code requires that transverse stiffener beams be used to provide some continuity. As with stringers, various wood species and mercial grades of deck laminations are available. Attachment of the deck to stringers is made by nails, spikes, or special fasteners. The structures may have decks running either perpendicular or parallel to bridges with longitudinal decks require transverse floor beams to support the deck and distribute load to longitudinal stringers. Diagrams of these structures are presented in Figs. 1 and 2. 河北联合大学轻工学院毕业翻译部分 18 Fig. 1. Stringer Bridge, deck perpendicular to traffic Fig. 2. Stringer Bridge, deck parallel to traffic Deck bridges can economically span to about 11 m (36 ft), and are from 200 to 400 mm (from8to16in.) deep (Fig. 3). The deck types are similar to those of the stringer bridge decks, with the addition of the continuous naillam deck, which is made of a single large panel, constructed on site. This deck type, as well as all of the stringer bridge deck types described previously, are considered 河北联合大学轻工学院毕业翻译部分 19 Fig. 3. Deck bridge Load Models Dead load typically constitutes from 10 to 20% of the total load effect on wood bridges. Dead load parameters are taken to be consistent with those used to calibrate the steel and concrete sections of the LRFD code (Nowak 1999, 1993). The considered statistical parameters include the ratio of mean to nominal (design) value, called the bias factor, λ , and coefficient of variation, V, that is the ratio of standard deviation to the mean. For wood and concrete (deck) ponents, bias factor λ = and coefficient of variation V=。 for steel (girders),λ = and V=。 and for asphalt, mean thickness is taken as 90 mm and V=. Dead load is taken as normally distributed. 河北联合大学轻工学院毕业翻译部分 20 Fig. 4. Bias factor for live load 河北联合大学轻工学院毕业翻译部分 21 Fig. 5. Coefficient of variation for live load As wood strength is affected by load duration, the live load duration is calculated for various time periods. Three values of the average daily truck traffic (ADTT) are considered: low with ADTT=500, medium with ADTT=1,000, and high with ADTT=3,000. It is assumed that the percentage of the actual heavy trucks (only very heavy vehicles need to be considered) is 20%,and this corresponds to 100, 200, and 600 trucks per day for the three considered traffic volumes, respectively. Note that these are high ADTT values for typ。