Parametric Design 

  Parametric Design of Load Bearing Masonry Buildings  
  Russell Gentry, Andres Cavieres and Tristan Al-Haddad
Georgia Institute of Technology School of Architecture
 
 

This article describes ongoing work on an NCMA Research and Education Foundation Grant, titled: Extending the Design Potential of Concrete Masonry Software. The research is being completed by Russell Gentry, Andres Cavieres, and Tristan Al-Haddad of the Georgia Institute of Technology.

Masonry construction is defined by the placement and bonding of individual modular units into a continuous load-bearing assembly. The geometric characteristics of this masonry continuum arise as design decisions are made by architects and engineers, and they solve a set of interrelated issues regarding structural stability, strength, functionality, aesthetics, cost and constructability.

Research, sponsored by the NCMA Research and Education Foundation, is developing software tools to help designers explore and understand the complexity of concrete masonry, and at same time to provide guidance to find more innovative geometric solutions (Figure 1). The basis for this research is the availability of new parametric modeling technologies that allow more intelligent representations of buildings models and provide greater power to generate and control complex geometries.

These are parametric models infused with information, and are thus widely described as building information models or BIM. BIM software like Digital ProjectTM, Tekla, Revit®, and Generative Components provide parametric capability as an expansion to traditional two dimensional CAD.

The problem with un-informed computer modeling is that many of the attractive forms that come out of the model are only feasible in the virtual space of a computer display, where there is no gravity or other real world constraints. Despite the powerful capabilities of these new computational technologies, design intent is limited by the lack of knowledge on how things really work in the physical world (Figure 2).

To address this issue we have focused on the development of methods to formally define the behavior of parametric masonry models, so that they bring the rules of masonry construction into the CAD design environment. In this manner objects representing CMU block, lintels, bond beams or reinforcements adapt and adjust themselves intelligently according to design changes and inform architects and engineers about the feasibility of their design (Figure 3). In this way, the structure is analyzed as it is designed, and the designer receives continuous feedback on the suitability of the structure.

Construction
Through the use of concrete masonry guidelines, for example, those provided by the NCMA TEK series, we identified a basic set of fundamental definitions and specifications for load-bearing masonry construction. Initially the research focused on placement of blocks according to bond patterns for flat and curved walls as well as for wall corbelling. Later we addressed structural implications of double curved walls and the interaction of reinforcement and different types of openings.

The identified construction and structural rules are translated into conceptual diagrams that capture the essential geometric aspects of masonry walls and help to specify how the smart parametric representations must behave. Figure 4 shows the example of a short design exercise where a curved wall with a screening effect is specified in terms of conceptual diagrams that clarify and document the rules for its further implementation as parametric models.

Structure
An important type of feedback that is provided to the user is the structural soundness of the design, especially at early stages of conceptual exploration. Embedded algorithms provide preliminary structural analysis to the architect and generate feedback in real time as the walls are created in the CAD environment. Figure 5 illustrates this process, which starts by subdividing a wall into slices.

These slices are sent to a Visual Basic script embedded in Excel that performs structural calculations and selects the appropriate vertical and bond-beam reinforcement for that segment of the wall. The calculations are simplified accordingly to basic needs and complexity of a conceptual model, so that the feedback can be made as quickly as possible. Based on the informed structural feedback to the architect, a more consistent and productive collaboration can be established between the architect and structural engineer.

Ongoing Work
Ongoing work is extending the set of rules already implemented, as well as the number and type of concrete masonry components. Integration with other building systems that are typically used with concrete masonry is being addressed, to expand the intelligence of the models to a wider scope of design and construction issues.

So far our team has established the basis for capturing and embedding concrete masonry construction knowledge into parametric models. The work foregrounds the advantages and great potential of CMU construction, as well as the value of the legacy knowledge and expertise embedded in masonry codes and guidelines (like the NCMA TEK Notes). We believe that new BIM tools will capture and deliver this knowledge to architects in the early stages of design—simultaneously educating and promoting the use of concrete masonry.

Further information on the technical aspects of our work can be found in these recent publications which are available from Russell Gentry (T.Gentry@coa.gatech.edu):

  • Andres Cavieres, Russell Gentry, and Tristan Al-Haddad, (2008), “Parametric Design of Masonry Buildings. Embedding Construction Knowledge,” Proceedings of the 2008 8th International Seminar on Structural Masonry (ISSM), Istanbul, Turkey—November 5-7, 2008.
  • Andres Cavieres and Russell Gentry, (2008), “Parametric Modeling of Masonry Assemblies”, Poster Session, Third International Conference On Design Computing And Cognition, Atlanta, Georgia, 21-25 June, 2008.
  • T. Russell Gentry, Andres Cavieres, and Tristan Al-Haddad (2009), “Parametric Design, Detailing and Structural Analysis Of Doubly-Curved Load-Bearing Block Walls”, 11th Canadian Masonry Symposium, Toronto, Ontario, May 31–June 3, 2009.

  • Andres Cavieres, Russell Gentry, and Tristan Al-Haddad, (2009), “Rich Knowledge Parametric Tools for Concrete Masonry Design: Automation of Preliminary Structural Analysis, Detailing and Specifications”, Proceedings of the 2009 26th International Symposium on Automation and Robotics in Construction (ISARC), Austin, Texas, U.S.—June 24-27, 2009. CMD

Click on the images for a larger view.

Figure 1: An architectural design showing a novel use of concrete masonry.

Figure 2: A parametric model showing complex geometry, but with little information on material properties, structural suitability, or constructability.

Figure 3: Algorithm to adjust window size and location to accommodate masonry coursework, and to adjust location of vertical reinforcement and bond beams to accommodate window placement. For curved walls, algorithm checks whether a planar window can fit within the curved wall opening.

Figure 4: A graphic representation of the parametric used to adjust the block as complex wall geometry is modified. The block wall adapts to maintain its running bond pattern and to limit the wall geometry to those shapes that can be achieved through corbelling.

Figure 5: Iterative structural analysis within the BIM system is achieved through a VBA link to Excel. When wall geometries are changed int he model, the structural analysis is automatically updated and provides wall reinforcement back to the BIM system.