This article highlights some useful guides that can be followed when preparing general arrangement drawings.
Structural layout drawings also referred to as general arrangement drawings or ‘GA’ are a type of drawings that showcases the arrangement of structural elements within a model. It’s a drawing that actively delineates the original disposition of these elements, providing a comprehensive visual representation. This drawing not only captures the essence of a layout but also actively communicates crucial information regarding the precise size and type of each structural element.
Generally, when a client requires a new structure, the procedure is to call an architect who receives the brief, this is true at least for building structures. The architect transforms the client brief into an architectural drawing showing floor plans, elevations and sections. In very rare circumstances such as where a brief requires an unconventional structure, the structural engineer might be available to assist the architect while developing the brief. This approach is good because it allows the structural engineer make input about the disposition of structural elements while the architect think about realizing the brief. However, this approach is sometimes time consuming hence it is seldom the case. In most of the instances, all the structural engineer receives are a set of drawings from the architect for him to prepare the structural drawing. Thus, the structural engineer is faced with the sometimes-uphill task of preparing a general arrangement drawing that must not only fully comply with the brief but must also be structurally viable.
Preparing a structural layout drawing is a much-underrated skill. It is a skill that can almost not be mastered in one or few attempts but only through consistent exposure to the subject. For the experienced design engineer, preparing the general arrangement drawing is unarguably the most important task in the structural design process. This process can be demanding just as it is imprecise, rightly so, a group of engineers can be given the same architectural drawing to prepare a structural general arrangement, and each of them will arrive at distinct solutions. On the surface, the distinctions in the solutions might not mean anything if they are all structurally viable, however when interrogated much more closely, an experienced engineer will be able to tell that some of the solutions are better than others.
Guides
In preparing structural layout drawings, there are no rules but guidelines. This is where a design engineer is expected to show competence by bringing to bare his conceptual design skills, based on knowledge of first principles. In training, a design engineer is taught that a design must be functional, structurally viable, economical, and above all, must be safe. Thus, in preparing the structural layout, structural engineers should always think along these lines.
Here are some generic guidelines that may aid in arriving at a very good structural layout:
Always Consider Functionality
In preparing structural layout drawings, paramount consideration must be given to functionality. The layout and arrangement of your structural elements must align seamlessly with the intended purpose of the structure. This involves a careful examination of spatial requirements, ensuring that the layout not only meets aesthetic and architectural goals but also facilitates efficient use of space. The structural general arrangement must account for the intended functionality of each space within the structure, enabling a harmonious integration of architectural and engineering aspects.
A common issue bothering on functionality in preparing structural general arrangements is columns appearing in spaces where the architect has clearly designated to be column free/uninterrupted spaces. When this happens, the architectural drawing and by extension the client brief has been violated. Hence, this should be strictly avoided. It’s better to propose an uneconomical scheme that achieves the brief than a scheme that does not satisfy the brief at all.
Opt for a Structural Viable Model
A critical aspect of creating structural general arrangement drawings is ensuring structural viability. A structurally viable model is a general arrangement that is, structurally stable and has a well-defined load path, and above all, safe. Attention to the distribution of structural elements, their connections, and load paths is essential to guarantee the overall integrity and longevity of a structure.
Choose a structural layout that produces a structural model that offers stability and resilience. The stability of a model is fundamental to the overall structural integrity of the structure. The disposition of structural elements should not result in an equilibrium problem or a situation that leads to a mechanism.
If the model is stable, precisely outline, define and consider the load path in the structural layout drawing. This involves illustrating how loads are transferred through various structural components, such as beams and columns, to the foundation. A clear depiction of the load path is crucial for ensuring that the structure can efficiently bear the intended loads without compromising safety. And always remember that the best structural layout with respect to load paths is the one that follows the shortest/direct route to the foundation.
Think About Buildability
Incorporating buildability into the preparation of structural general arrangement drawings is crucial for a smooth construction process. This entails considering practical aspects such as construction sequence, site access, and the availability of materials. The general arrangement should be structured in a way that minimizes complexity during construction, promotes efficient assembly, and ensures that the construction team can execute the design without unnecessary complications.
While a layout might be functional and structural viable, it is not advisable to select a structural layout on that basis alone. A good structural layout must also cognize buildability. For instance, between a complex transfer slab and simple transfer beams which is easier to build? While the complex transfer slab might actually be functional and structurally viable, not all contractors are able to handle a transfer slab which no doubt will require some specialized equipment and tact attention to details. On the other hand, transfer beams may easy be built. Thus, in preparing the structural general arrangement drawing, a good design engineer must also think about the expertise of the contractor that would likely handle implementation.
Think About Economy
The last but by no means the least consideration in the preparation of structural layout is economy. Every structural design must strike a balance between structural integrity and cost-effectiveness. Thus, in preparing the structural layout drawing, you must think about economy. For instance, between a layout that proposes a whole transfer slab level and one that simply proposes transfer beams, which would be economical? Again, while a transfer slab might be more functional and structurally viable, in many instances a transfer beam is more cost effective.
Thus, in preparing the structural layout be cognisant of the economic consequences associated with the structural arrangement. Assess the financial impact of your choices and consider how they may influence the overall cost of the project. Simultaneously, analyze the structural implications to guarantee that the chosen arrangement aligns with safety standards and long-term structural durability.
Also See: Structural Design Guidelines and Methodology
Conclusion
In conclusion, the preparation of structural layout drawings requires a thoughtful and systematic approach. As aforesaid, this is a skill that one can only achieve mastery through experience. There are no rules. In fact, what makes the preparation of general arrangement drawings more problematic is that the guidelines rarely converge. For instance, when comparing two structural layouts, it is almost impossible for one of them to supersede the other with respect to functionality, structurally viability, buildability and economy. It’s either one of them is more functional and structurally viable while the other is more economical and buildable. However, striking a balance between the guides will always result in a very good structural layout drawing.
