Advanced Approach To Vibration Analysis

PERFORMING A MODEL ANALYSIS AND CALCULATING THE DYNAMIC RESPONSE OF THE FLOOR USING FEM MODEL

Working on the design of the six-story mass timber building project in the US, we did a detail vibration analysis of the floor slabs of this building to achieve maximum precision and optimize the structure. The complete building is designed as mass timber frame system structure with GL beams and columns and CLT floor and roof slabs which we detailly analyzed for the governing vibration requirement.

Traditional building methods with concrete as the main building material result in heavy floor structures while lightweight floor structures could be made out of steel, lightweight concrete or timber. The development of lighter floor structures is driven by the aim to be more efficient and use less materials, as well as to use materials that are considered environmentally friendly, such as timber.

In order to calculate as precisely as possible the dynamic properties and response of the floor and to optimize the structure, we use FEM model and FEM analysis.

Performing a modal analysis offers several benefits, including:

Thickness reduction of CLT slabs: Modal analysis allows for the precise determination of the dynamic response of the structure. This information enables engineers to optimize the thickness of CLT (Cross-Laminated Timber) slabs, potentially reducing material usage while maintaining structural integrity.
Consideration of slab shape: The shape of the slabs plays a significant role in the analysis results. Modal analysis takes into account the geometry of the structure, which is often overlooked in early-stage design using guideline methods. By considering the slab shape, more accurate results can be obtained.
Influence of connection rigidity: The rigidity of connections between beams and columns, as well as between CLT panels and beams, has a notable impact on the analysis results. Guideline methods rely on simplified assumptions and formulas, which do not consider the global model. Modal analysis provides a more comprehensive assessment by accounting for connection rigidity.
Accurate finite element model: Modal analysis requires an accurate finite element model of the structure to predict the dynamic response. This level of detail enables precise determination of the optimal thickness for CLT slabs. Compared to guideline methods, modal analysis is considered the most accurate method of analysis.
Assessment of floor response: Modal analysis incorporates various factors, such as walking paths, forcing functions, and specific response points on the floor where vibration measurements are desired. This comprehensive approach allows for a precise assessment of floor response to dynamic loads.