谈中小桥采用后张法16m预应力空心板的施工问题

本文阐述了中小桥上部结构采用后张法１６ｍ预应力空心板的施工时应注意的问题，如预应力空心板的预制中底模的施工；侧模、蕊模；砼的要求；浇筑空心板的具体步骤。     

浅析跨径20m预应力空心板内模变换的方法

文章结合跨径20m预应力空心板预制的施工管理实践，介绍预应力空心板内模变换的一种方法及施工工艺。     

预应力混凝土空心板"蒸养"裂纹产生与防范

在预应力空心板冬季“蒸养”过程中，混凝土初期养护管理、升降温梯度、板粱上下散热速度差以及梁内是否配置防裂钢筋等都将对粱的浇注质量产生影响，本文以伊嘉公路五汤段的预应力空心板粱为例，对粱的“蒸养”裂纹作了详细分析，提出了相应的防范措施。     

斜预应力空心板施工裂缝控制

通过对预应力空心板施工裂缝的调查总结,对斜预应力空心板施工裂缝产生的原因进行了分析,并提出了制定预防裂缝的具体措施。     

大跨度预应力混凝土空心板

大跨度预应力混凝土空心板大跨度预应力混凝土空心板（简称ＳＰ板）是华霖现代建筑材料有限公司全套引进美国ＳＰＡＮ－ＣＲＥＴＥ公司生产线设备、专利技术生产的一种新型建材产品。该产品采用高强度低松弛钢绞线为预应力筋，主机对干硬性混凝土冲捣、挤压一次成型的新工...     

预应力空心板先简支后连续受力性能研究

先简支后连续结构,不仅具有简支梁桥施工简便的优点,而且保证桥梁的行车平顺。本实验基于预应力空心板先简支后连续的结构特征和受力特点,进行荷载试验和极限承载能力的加载试验,同时与预应力简支空心板作对比试验。试验结果表明,先简支后连续结构明显优于桥面连续的结构。     

先张法预应力混凝土空心板施工质量监控分析

嵩待高速公路七合同段K62＋111（3—20）桥为先张法预应力钢筋混凝土空心板梁桥。本文以此为切入点，详细阐述二横梁槽式台座内预应力钢绞线单股逐根张拉设备及夹具选用、铜绞线张拉前的准备工作、张拉的步骤和方法、钢绞线放张和切断的原则及顺序等。分析先张法预应力钢筋混凝土空心板在施工过程中台座、张拉设备、控制应力及张拉程序等质量控制问题。就现场施工过程中出现的钢绞线磨损严重、夹片损坏严重、钢绞线实际伸长值达不到要求、钢筋混凝土横梁开裂、空心板预拱度无法达到要求等这些关键性问题的解决补救措施进行简要分析。     

大跨度SP预应力混凝土空心板结构检验

大跨度ＳＰ预应力混凝土空心是采用美国ＳＰ公司技术与设备的一种新型预应力混凝土材料,具有很多优点,填补了国内大跨度板的空白,对其进行结构性能检验是非常重要的。     

先张法预应力空心板纵向开裂的防治

多年来先张法预应力空心板在中、小桥结构物中一直被广泛应用.但在设计回访中发现,部分空心板板底多存在有纵向裂缝的问题,为有效杜绝此弊病的发生,本文对其产生的原因进行了分析并提出了预防措施.     

大跨度预应力空心楼盖的施工抗浮

对大跨度预应力空心楼盖的施工抗浮问题，从施工过程的发生、发展以及抗浮的受力分析、抗浮的处理方法等作了深入的研究，对该类问题的施工解决提出了新的可行的办法。减少了施工的盲目性，减少了大跨度通情达理应力空心楼盖抗浮施工时各种质量问题的发生，填补了“空心管＋预应力”技术在施工应用方面的一项空白。     

番龙眼地板毛坯干燥工艺基准和干燥工艺实施

为了提高番龙眼地板毛坯干燥质量,对25mm厚的番龙眼地板毛坯进行低温低湿干燥工艺的研究.探讨了番龙眼木材干燥工艺基准的制订,并通过番龙眼木材干燥工艺的实施对其干燥结果进行分析,为进一步研究制订番龙眼木材干燥工艺提供了思路和方法.     

Presence of longitudinal cracks in planks from storm-felled pine (Pinus sylvestris L.) and spruce (Picea abies (L.) Karst.)

Abstract

After the severe storm Gudrun in southern Sweden in 2005, a quantitative study was done in order to investigate the presence of lengthwise crack on planks taken from storm-felled trees in southern Sweden, compared to planks from standing trees not subjected to this storm (central Sweden). The main yield from each log was examined. In total, 1087 pine (Pinus sylvestris) planks and 3626 spruce (Picea abies) planks from the storm-struck area were investigated and compared to 1953 spruce and 2000 pine planks from trees outside the storm-struck area. The examination of cracks was done visually on dried planks. For pine, 51.7% of the planks from storm-felled trees had a total length longer than 0.5 m, compared to 7.3% for the reference material. As for spruce, 11.0% of the planks from storm-felled trees had a total crack length of more than 0.5 m, compared to the reference material where 2.2% had cracks longer than 0.5 m. The results show that the storm-felled trees had more longitudinal cracks than the reference material and that pine was more likely to develop storm-related cracks than spruce.     

Influence of provenance,silvicultural regime and tree shape on the quality of maritime pine (Pinus pinaster) timber

The aim of this study was to establish the sources of variation in maritime pine wood properties related to appearance and strength, because of the importance of this wood in the sawing industry in Galicia (NW Spain). Ten trees from each of ten plots of the species (i.e., 100 trees) growing in Galicia were felled and sawn to produce the structural planks required for studying the presence of external strength-reducing characteristics. The planks were sampled from the basal logs to 16 m height in the stems, yielding cross sections of target dimensions 100 × 40 mm to 200 × 200 mm. We propose a model in which individual tree height and dominant height are used to predict the knottiness of planks from trees in mature stands. The abundance of externally visible knots on faces and edges of sawn planks is therefore more dependent on the stand location than on the prior silvicultural treatment of the stand.     

Multivariate product adapted grading of Scots Pine sawn timber for an industrial customer,part 2: Robustness to disturbances

ABSTRACT

Holistic-subjective automatic grading (HSAG) of sawn timber by an industrial customer's product outcome is possible through the use of multivariate partial least squares discriminant analysis (PLS-DA), shown by part one of this two-part study. This second part of the study aimed at testing the robustness to disturbances of such an HSAG system when grading Scots Pine sawn timber partially covered in dust. The set of 308 clean planks from part one of this study, and a set of 310 dusty planks, that by being stored inside a sawmill accumulated a layer of dust, were used. Cameras scanned each plank in a sawmill's automatic sorting system that detected selected feature variables. The planks were then split and processed at a planing mill, and the product grade was correlated to the measured feature variables by partial least squares regression. Prediction models were tested using 5-fold cross-validation in four tests and compared to the reference result of part one of this study. The tests showed that the product adapted HSAG could grade dusty planks with similar or lower grading accuracy compared to grading clean planks. In tests grading dusty planks, the disturbing effect of the dust was difficult to capture through training.     

Rectangularity of planed Scots pine (Pinus sylvestris) planks

Abstract

This study deals with how warp affects the cross-sectional shape of planed planks. A total of 20 planks with dry target cross-sectional dimensions of 50×150 mm were planed to 45×145 mm. The rectangularity of five cross sections of every plank was measured before and after planing. The cutting depths were measured in 10 positions in the cross sections, and the angles between the planks and the cutters were calculated. Also, the warp, that is, twist, bow, crook, and cup, was measured before and after planing. All the studied properties pointed in the same direction. In terms of both rectangularity and angles of cut, the problems were larger in the top and butt ends of the investigated planks than in the intermediate parts, and the main reason for deviations from the desired result after planing was twist.     

Multivariate product adapted grading of Scots pine sawn timber for an industrial customer,part 1: Method development

ABSTRACT

Rule-based automatic grading (RBAG) of sawn timber is a common type of sorting system used in sawmills, which is intricate to customise for specific customers. This study further develops an automatic grading method to grade sawn timber according to a customer's resulting product quality. A sawmill's automatic sorting system used cameras to scan the 308 planks included in the study. Each plank was split at a planing mill into three boards, each planed, milled, and manually graded as desirable or not. The plank grade was correlated by multivariate partial least squares regression to aggregated variables, created from the sorting system's measurements at the sawmill. Grading models were trained and tested independently using 5-fold cross-validation to evaluate the grading accuracy of the holistic-subjective automatic grading (HSAG), and compared with a re-substitution test. Results showed that using the HSAG method at the sawmill graded on average 74% of planks correctly, while 83% of desirable planks were correctly identified. Results implied that a sawmill sorting station could grade planks according to a customer's product quality grade with similar accuracy to HSAG conforming with manual grading of standardised sorting classes, even when the customer is processing the planks further.     

A new proposal to reinforce planked timber shear walls

Timber is one of the most common materials used in traditional buildings worldwide. Our previous research has suggested that timber shear walls play an important role in resisting external loadings, such as earthquakes. Thus, improving the structural performance of in-filled shear walls can also improve that of the entire structure. In the traditional Taiwanese timber shear wall system, the embedment strength of beams and friction between wooden planks and beams significantly affect the strength of the shear wall. This article proposes a new method of reinforcing traditional timber shear walls in Taiwan by inserting teak and padauk strips into the grooves between wooden planks and beams to increase the embedment strength of beams and the friction between wooden planks and the hardwood strips. A total of 18 full-scale specimens were tested under reversed cyclic loading. The results revealed that the strength and energy dissipation capacities of a wooden shear wall can be significantly increased by inserting teak and padauk strips into the grooves between planks and beams. Furthermore, the simplified calculation method proposed in this study can be used to calculate the strength of both reinforced and unreinforced wooden shear walls with satisfactory agreement.     

A fracture mechanics approach to the tensile strength perpendicular to grain of dimension lumber

Summary Six hundred short sections taken from 23 flatsawn 2x12-inch planks of construction grade Doughas-fir were tested in tension perpendicular to grain. Most of the specimens contained defects in the form of checks, knots, resin streaks, pitch pockets, and pith. Checks were found to be the major strength-reducing defect. The effect of checks could be analyzed effectively by using the concepts of fracture mechanics.     

Variation in log quality and prediction of sawing yield in oak wood (Quercus robur)

Context

The commercial feasibility of sawmilling depends on the expected volume and value of sawn planks. Models that predict the volume of sawn timber of a particular quality and produced from logs of known characteristics are therefore very useful.

Aims

The objectives were to study variation in sawing yield and to obtain models that predict lumber volume and grade recovery on the basis of easy-to-measure predictor variables of saw logs.

Methods

Forty-six oak trees growing in Galicia (NW Spain) were felled and cut into logs. The logs were visually graded and sawn mainly into quartersawn planks, which were dried, planed and visually graded for structural purposes.

Results

The total volumetric sawing yield was 47.6 %. The sawing yield for planks of structural dimensions (cross-section, 70?×?120 or 70?×?170 mm) was 43.4 %, but decreased to 8.4 % for structural sized and quality grade beams because of wane and biotic damage in many pieces. Log grade did not significantly affect sawing yield in the sample analysed, despite the wide range of diameter over bark at the smallest end in the sampled logs (22–77 cm). The sawing pattern affected total sawing yield (F?=?4.913; p value?=?0.001) and the sawing yield for structural planks (F?=?6.142; p value?=?0.0002); radial sawing with one cut and live sawing of half logs provided the highest yields. Three models were proposed for estimating sawn volume in timber products, with the small-end log diameter over bark as the predictor variable and R _adj ² between 0.31 and 0.78 (p value?<?0.01).

Conclusion

For the purpose of producing oak timber destined for structural use, the presence of bark and sapwood in planks must be reduced in the sawing process; this would decrease the total lumber recovery but increase the timber value yield. Air drying must be accelerated to reduce biotic damage in sawn planks. Geometric mean diameter over bark at the smallest end (d) outperforms other measures as a predictor variable for total or structural sawn timber volume.     

光栅投影测量技术在毛边板优化裁边中的应用

提出了采用基于光栅投影的三维测量技术,以获取毛边板的较高精度轮廓数据,对优化毛边板裁边工艺、提高木材出材率具有重要意义.