Modelling and Characterization of the Structural Behaviour of Wooden Cultural Heritage under Hygro-mechanical Loading

木质文化遗产，如历史板画、家具和乐器，往往会出现大变形和裂缝。原因是由于室内气候的每日和季节变化以及机械负荷(例如，由于乐器弦张紧造成的)而产生的水力负荷。在该项目的框架内，应能够对这些荷载下的木结构进行长期分析，从而开发一种客观的工具，以便在保护的背景下作出决策。可以确定和研究临界荷载以及修复措施对结构响应的影响，而不会影响唯一的原始对象。通过预测木制品在未来载荷和气候变化下的长期行为，并通过定义可容忍的气候条件限制，该分析工具可以为历史木质文化遗产的保护做出重要贡献。对于用有限元方法对木制品进行全面的长期结构分析，开发有效的方法来考虑随时间变化的气候载荷和结构响应是必要的。为了能够模拟长期范围内的大型结构和高度非线性的材料模型，需要显著降低计算成本。因此，开发了一种时间多尺度方法，用于描述木材的胞状、天然材料、多物理特性以及水分和机械外部载荷。在该项目中，开发了描述木材随时间和水分变化行为所需的本构材料公式。通过适当的实验，研究了湿气引起的应力、蠕变效应以及粘接接头和表面涂层对水分传输和力学结构行为的影响。到目前为止，历史文物中使用的特征木材树种、历史胶水和表面涂层的随时间、湿度和载荷依赖的蠕变和机械吸附效应以及微观水分传输的材料特性是在考虑自然变化的情况下通过实验确定的。在这些实验的帮助下，得出了适当的物理规律，并建立了材料模型。新开发的方法和模型被用于历史物体的数值模拟和结构分析。通过有限元分析，得到了多种物理载荷和材料特性对承载性能的影响。实验和模拟的结果被用来定义博物馆内不会对文化遗产造成或加剧破坏的室内气候的合理变化，从而成为保护人员评估气候影响和预测历史文物结构长期行为的潜在工具。

Wooden cultural heritage, like historical panel paintings, furniture and music instruments often show damages as large deformations and cracks. The reason are hygrical loadings, that occur due to daily and seasonal variation of the room climate and mechanical loadings, e.g. resulting from tensioned strings of instruments. Within the framework of the project, the long-term analysis of wooden structures under these loadings shall be enabled and, thus, an objective tool developed for decision making in the context of conservation. Critical loadings as well as effects of restoration measures on the structural response can be determined and investigated, without influencing the unique original objects. By predicting the long-term behaviour under future loadings and climate change and by defining tolerable climate conditional limits, the analysis tool can be an important contribution to the preservation of the historical wooden cultural heritage.For the comprehensive long-term structural analysis of wooden objects by the Finite-Element-Method, the development of efficient methods is necessary to consider time-dependent climate loads and structural responses. To enable the simulation of large structures in the long-term range and highly non-linear material models, the computational costs need to be considerably reduced. Thus, a temporal multiscale method for the cellular, natural material wood, the multi-physical characteristics and hygrical and mechanical external loadings is developed.The required constitutive material formulations for the description of the time- and moisture-dependent behaviour of wood are developed within the project. The moisture-induced stresses, creep effects as well as the influence of adhesive joints and surface coatings on moisture transport and mechanical structural behaviour are studied with the help of appropriate experiments. The, until now, widely unknown material properties for time-, moisture- and loading-dependent creep and mechano-sorptive effects as well as micro-scale moisture transport of characteristic wood species, historical glues and surface coatings, used in historical objects, are determined experimentally under consideration of the natural variation. Appropriate physical laws are derived and material models are developed with the help of these experiments.The newly developed methods and models are used for the numerical simulation and structural analysis of the historical objects. The influence of multi-physical loadings and material characteristics on the load-bearing behaviour is captured by means of Finite-Element-Analyses. The results of the experiments and simulations are used to define reasonable changes of room climate within museums that do not cause or intensify damages to the cultural heritage and with that are a potential tool for conservators to evaluate the influence of the climate and predict the structural long-term behaviour of historical objects.