Analysis of Planar Double-Layer Timber Spatial Frames by Using Parametric Tools

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Timber construction is a popular structural system because wood has a high strength-to-mass ratio and low carbon footprint. Timber buildings have an increasing capacity toward taller designs and more flexibility that attracts researchers’ interest. Therefore, the topic of the presented study is relevant. The traditional goal of all designers in the construction industry is to develop a design for a building element using the minimum amount of material and at the same time ensure that the conditions of strength, rigidity and stability are met. The team of authors offers a specific software tool for parametric design of flat two-layer spatial grids. The obtained result has practical value for quick and accurate execution of the stage of preliminary design of planar double layer timber frames structures.

 There are comments and recommendations regarding the text of the manuscript.

 1. In the first section of the manuscript, "1. Introduction", the authors made a good overview of the research topic from the point of view of practical application. But unfortunately, they practically ignored citing scientific literature published over the past five years in the direction of the research being conducted. This situation needs to be corrected.

 2. Is it possible to customize the proposed software tool so that the results do not exceed the limits of state building codes? What are the main limitations of using parametric software (Grasshopper and Karamba 3D) for the design of timber frame constructions? I think this needs to be mentioned in the text.

 3. A structural engineer often has to deal with medium-span rectangular roofs. What are the key structural performance indicators and metrics that need to be considered when analyzing the behavior of double-layer timber spatial frame constructions for such roofs (medium-span rectangular roofs)?

 4. What criteria do you set for a computer to implement parametric design (in order to ultimately obtain the optimal result)?

 5. You use several hypotheses and simplifications: about the application of load, about wind loading, you consider modeling connections as simple joints, despite their inherent transfer of moment in reality, etc. The summation of such inaccuracies can lead to the fact that a wonderful design project will be impossible from the point of view of a construction engineer. How to protect yourself from such situations?

Comments for author File: Comments.pdf

Author Response

Comment 1. In the first section of the manuscript, "1. Introduction", the authors made a good overview of the research topic from the point of view of practical application. But unfortunately, they practically ignored citing scientific literature published over the past five years in the direction of the research being conducted. This situation needs to be corrected.

Response 1. A paragraph has been added to explain current research directions with its related bibliography.

Comment 2. Is it possible to customize the proposed software tool so that the results do not exceed the limits of state building codes? What are the main limitations of using parametric software (Grasshopper and Karamba 3D) for the design of timber frame constructions? I think this needs to be mentioned in the text.

Response 2. The results presented in the work fulfill the standards Established in the Technical Building Code (the requirements are shown in Table 1). In fact, in the results graphs, the non-compliant meshes are not represented. This illustrates the limits of each topology.

Comment 3. A structural engineer often has to deal with medium-span rectangular roofs. What are the key structural performance indicators and metrics that need to be considered when analyzing the behavior of double-layer timber spatial frame constructions for such roofs (medium-span rectangular roofs)?

Response 3. The results have been organized keeping architects and engineers in mind. Taking into account legal requirements and material economy, three indicators are defined for analysis and comparison between topologies: mass-deformation ratio, exhaustion rates and metrics (nodes and bars).

Comment 4. What criteria do you set for a computer to implement parametric design (in order to ultimately obtain the optimal result)?

Response 4. 

Karamba 3D offers several components for the optimization of results. In the paper the two main ones are proposed: cross section optimization and genetic algorithm

Cross section optimization: it selects the most suitable section dimensions in each case from all the possible ones (list established in the data input).

Genetic alhorithm (galapagos): this component is wider than the previous one. Genetic algorithm (galapagos) works with 2 outputs: one or several genome(s) and a single fitness. The latter is the value to be minimized or maximized, and for this purpose the program finds the appropriate value of the genome(s). There are many possibilities for the relationships between data that can be established with this component. In this case, a relationship of interest is established for spatial frames: genomes: structural depth - fitness: mass

By combining both components, optimized results are achieved.

Comment 5. You use several hypotheses and simplifications: about the application of load, about wind loading, you consider modeling connections as simple joints, despite their inherent transfer of moment in reality, etc. The summation of such inaccuracies can lead to the fact that a wonderful design project will be impossible from the point of view of a construction engineer. How to protect yourself from such situations?

Response 5. 

The requirements in terms of quantity, accuracy and speed of information flow are different in each phase of a project. This work should be understood to be located in the preliminary design phase of the project. The numerical results in the file are approximate. Before reaching the construction phase, the basic and executive project will rigorously and thoroughly develop the designed structure.

 

The possibility to export the model to a more comprehensive analysis software (like RFEM Dlubal for example) also facilitates an exchange between both programs. You can perform the first design drafting in Grasshopper+Karamba 3D and then export it to Dlubal to check the numbers more accurately. Each program has its own particularities and the proposed methodology aims to make them useful in their way.

Reviewer 2 Report

Comments and Suggestions for Authors

The topic of the work is interesting, but the work has no scientific value. It is more of a program manulal than a scientific article. Please pay more attention to the structure analysis than to the computer program. The input and output data should be more extensive. Conclusions should be summarized,

Comments on the Quality of English Language

Some sentences are grammatically incorrect and need to be corrected thoroughly.

Author Response

Comment 1. The topic of the work is interesting, but the work has no scientific value. It is more of a program manual than a scientific article. Please pay more attention to the structure analysis than to the computer program. The input and output data should be more extensive. Conclusions should be summarized,

Response 1. 

The requirements in terms of quantity, accuracy and speed of information flow are different in each phase of a project. This work should be placed in the preliminary design phase.

Parametric tools (Grasshopper and Karamba 3D) offer a promising opportunity for a first structural analysis. Since the file is created by the designer himself/herself, is very similar to a manual process, and so offers a great deal of control and awareness. It is therefore necessary to explain in the paper the working methodology and the conceptual functioning created in the program.

In those first attempts where the unknowns are greater than the certainties, the information offered by these tools enables a technical argumentation. It is understood that the process should be as agile and dynamic as possible, in order to narrow down and define the geometry that deserves a deeper and more comprehensive development in other software (such as RFEM Dlubal for example). Extending the input and output data would overload the file making it slower and more tedious.

However, the conclusions are extended to illustrate the large amount of useful information that can be extracted from the file. Thus demonstrating its usefulness. 

Reviewer 3 Report

Comments and Suggestions for Authors

This is a very well written, illustrated and referenced paper. Spaceframe structures, especially from wood, are a very important subject of research, to reduce material consumption and increase material utilisation. Using a parametric tool like Grasshopper and even evolutionary optimisation is a very promising approach. Structural Analysis has been carried out in RFEM, although i would have liked to see more details on exactly how it was modeled. This makes a big difference for timber structures and it would make much sense to confirm results with physical tests. In my opinion this is neede for timber structures, especially more complex ones like spaceframes. MAybe you can improve this but i recommend accept anyway.

Author Response

Comment 1. 

This is a very well written, illustrated and referenced paper. Spaceframe structures, especially from wood, are a very important subject of research, to reduce material consumption and increase material utilisation. Using a parametric tool like Grasshopper and even evolutionary optimisation is a very promising approach. Structural Analysis has been carried out in RFEM, although i would have liked to see more details on exactly how it was modeled. This makes a big difference for timber structures and it would make much sense to confirm results with physical tests. In my opinion this is neede for timber structures, especially more complex ones like spaceframes. MAybe you can improve this but i recommend accept anyway.

Response 1. We take up this suggestion, which is definitely interesting, for future publications.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Some additions have been made. The authors have provided extensive sufficient explanations.