Montgomery Auto – Composite Steel Structural System

Location: Conroe, Texas

Program:

This function of this building will be a service center for automobiles and RV’s including but not limited to oil changes, state inspections and mechanical service. The building is two-stories with the bottom story being a basement (highlighted in yellow below).

Structural System:

Basement (Pit) – Cast-in-place concrete walls with isolated spread footings for the interior columns.

Structural Floor Above Pit : Composite concrete deck with 1½ composite metal deck with 4½” of reinforced concrete for a total thickness of 6″. The composite deck is supported by composite structural steel beams which frame into structural steel columns and the cast-in-place concrete basement walls.

Level 1 Slab: Stiffened slab-on-grade.

Superstructure: Metal Building System.

Unique Design Criteria:

The elevated floor of the pit needed to be designed to support a Class A RV which  based on our research indicated a 26,000 pound total weight. We utilized the AASHTO HS-10 (bridge design) weight distribution formula which assigns 80% of the weight to the rear axle and 20% to the front axle/ This resulted  in a design vehicular wheel load of 10,400 pounds on a minimum contact area of 150 square inches.

Composite Structural Steel Beams:

View our blog about composite construction at the following link: Composite Construction

Project Photos:

  

Composite Structural Steel Beams and Deck

Structural Behavior:

Composite construction refers to two load-carrying structural members that are integrally connected and deflect as a single unit. For composite beams, the two load carrying members are the structural steel beam and the concrete on composite metal deck with the shear studs being the element that connects them.

Utilizing composite action creates a stiffer, lighter and less expensive structure than if the two elements were not integrally connected and makes this system one of the choice options for commercial construction.

Composite Deck:

Typically accompanying composite steel beams is composite deck. Composite deck utilizes the steel deck and the concrete slab to form an integral unit that plays upon the concretes compressive strength and the steel decks high tensile strength. The element that integrally connects these two components are the steel embossment in the metal deck.

Advantages of Composite Construction

  • Reduced structural steel frame cost compared to non-composite steel construction.
  • Reduction in time and labor cost due to composite deck serving as both the form deck (which in most cases does not require shoring) and the positive reinforcement in the final structure.
  • Compared to cast-in-place construction which requires shoring and re-shoring, composite construction can drastically reduce the construction schedule.
  • Reduction in weight of structural steel frame which also can lead to a less costly foundation.
  • Reduced live load deflection and improved vibration performance due the composite construction being stiffer than comparable systems.
  • Potential for shallower beams which can reduce building height.
  • Increased span lengths are possible.

Disadvantage of Composite Construction

  • Material cost typically higher compared to cast-in-place concrete systems.
  • Installation of shear connectors requires specialized equipment (automatic stud welders) which typically mean having to bring on a speciality sub-contractor.
  • Introduction of camber can create issues with concrete levelness and finishing.

Shear Stud Installation:

Structural Diagnostics : Assessing Fire Damage

Foundation Exposed to Intense Fire

Dudley Engineering was engaged to perform a structural assessment of a foundation in Bryan, Texas that has been exposed to an intense fire. The 4-Alarm fire resulted in a complete loss of the superstructure and wisely the owner engaged Dudley Engineering to ascertain whether the foundation was damaged, prior to rebuilding.

Principal, Bryan Tyson, PE led the assessment which consisted of a visual assessment of the foundation including:

  • scorch marks
    • Smoke stains and scorch marks are typically good indicators of areas that were exposed to high heat and require further evaluation (see sounding hammer below)
  • cracks
    • Concrete exposed to high heat and then subsequently doused with water as is typical in a normal structural fire, can lead to drastic temperature changes and hence quick expansion and contraction of concrete leading to cracks. Consider placing a glass in the freezer and then subsequently removing it and running hot water over it, it will crack (not that we have ever done that before).
  • changes in color
    • A change in the color of the concrete may indicate that the concrete was exposed to heat exceeding 550°F. Concrete exposed to temperatures above 550°F often turn a shade of pink which indicates that a chemical change has occurred in the iron-containing aggregates and cement paste.
  • surface spalls
    • High heat can cause the pore water in the concrete to evaporate which can lead to spalling of the concrete.

The assessment also included testing of the concrete via a sounding hammer. A sounding hammer can be used to compare the resonance of the concrete after it is struck by the hammer. Healthy concrete will exhibit a sharp, high-frequency ringing sound when struck, while damaged or poor-quality concrete will typically exhibit a dull thud or soft noise.We, in corroboration with may documented cases, have found the sounding hammer technique to be a reliable and cost-effective means of assessing damage to concrete in the wake of a fire. The sounding hammer can also be used for destructive testing to assess the strength of the concrete. Healthy concrete will be unphased by a couple blows from a sounding hammer while heat-damaged concrete will crumble away with a few rigorous hits. Additionally the fracture mechanics of heat-damaged concrete is unique in that the fracture plane will typically form around the aggregate as opposed to directly through the aggregate, which is characteristic of healthy concrete.

To learn more about Dudley Engineering’s Structural Assessment / Diagnostics capabilities click on the link. 

Chalky Cement Paste – Indicative of Heat-Damaged Concrete
Spalling Concrete with Pink Color Tones – Fracture Plane Around Aggregate Pieces
Pink Color Change of Concrete

Metal Plate Connected Wood Trusses

Metal Plate Connected Wood Trusses – From Design to Fabrication

We were recently invited to go on a tour of Trussworks, LLC plant in Caldwell, Texas. Seeing the fabrication process and speaking with the truss design manager, Timothy McPeck and general manager, Justin Groom was a great learning experience. Blending the metal-plate connected wood trusses into the structural frame can provide an economical and safe solution for any project of Type III or V construction, however it requires the structural engineer-of-record and architect to have a solid understanding of the capabilities and limitations, this tour certainly put Dudley Engineering LLC a step ahead.

We have completed multiple projects with Trussworks and have found them to be a great partner is helping deliver successful projects.

Wood trusses are common in Multi-Family and light Commerical projects. They have the capability to span large distances while still leaving room for MEP which avoids the need for a drop ceiling.

Floor Truss Assembly Line
Roof Truss Assembly Line

Floor Truss Jig

Sway Bee Caves – Thai Cuisine

A Blend of Fine Dining and Innovative Design and Construction

Dudley Engineering blended the cold-formed steel design with the structural steel frame to provide a robust and economical structural system. The structural system consisted of cold-formed steel diagonal strap braced X-bracing lateral system, cold-form steel and structural steel roof joists, cold-form steel roof trusses, and composite structural steel beams with composite metal deck.

The use of cold-formed steel cut down the construction schedule as well as material and labor costs since all the members can be handled by a single laborer and connections can be completed via metal screws in lieu of welding or bolting.

Project Manager: Drew Dudley, PE

Location:

Photos

Example of Structural Drawings

Contact Drew Dudley, PE at ddudley@dudleyengineering.com for more information or to view a full set of the structural plans.

First Baptist Church – Huntsville, Texas

First Baptist Church Family Life Center

Huntsville, Texas

About

Dudley Engineering provided structural engineering and building envelope design, consulting and inspection for this church facility which consisted of structural steel framing, cast-in-place concrete basement walls, cold-formed metal framing stud walls and brick veneer. We enjoyed getting to spend time in Huntsville and especially enjoyed getting to eat at the nearby Farmhouse Cafe (@farmhousecafehuntsvilletx) which never disappoints.

Multi-Family Development | Spring, Texas

Project Description

Dudley Engineering provided the structural engineering design for the foundation and superstructure of this multi-family development in Spring, Texas.

In collaboration with Moment Architects, Dudley Engineering sought to reduce the structure cost by utilizing advanced framing techniques and engineered wood products.As part of our full-service approach, Dudley Engineering also provided construction administration and inspection services to verify construction.

Location

Kuykendahl Road and Gosling Road | Spring, Texas

Additional Information

Read more about our multi-family expertise here: Dudley Engineering Multi-Family Service

 

Drew Dudley, PE Honored as Rising Star in Structural Engineering by Civil + Structural Magazine

Drew Dudley, PE was honored as 1 of 13 recipients to receive the Rising Star in Structural Engineering award from Civl + Structural Magazine which recognizes professional 40 years old or younger working in the United States, who have shown exceptional technical capability, leadership ability, effective teaching or research, or public service benefiting the civil and structural engineering professions, their employers, project owners, and society.

Link to Civil + Structural Magazine Article

Limiting Concrete Cracks: Re-Entrant Corners


Whether you are a contractor, architect, engineer or simply a home owner with a concrete foundation you have most likely heard the adage that “all concrete cracks”. While this is true, there are measures that can be taken to greatly reduce the magnitude and frequency of cracks. To do this, one must have an understanding of the factors that lead to cracking. One such factor is stress concentrations in the concrete which are evident at re-entrant corners. Re-entrant corners are defined as any inside corner that forms an angle of 180° or less. In a solid object that is subjected to internal or external loads, re-entrant corners create high stress concentrations. If that solid object is concrete, which is strong in compression but weak in tension, then it will inevitably lead to a crack that will propagate at approximately 135° from the corner. Re-entrant corner cracks are especially prevalent in concrete slabs that are relatively thin in comparison to their plan size. In this article, I will focus on re-entrant corners in slabs-on-grade.

Examples of loads that can induce stress in concrete slabs include:

Shrinkage of the slab during the curing process when the concrete will shrink in volume as the chemical reaction between the cement and water takes place. Depending on the curing methods in place, the top and bottom surface of the slab will cure at different rates which induces stress in the slab.
Temperature changes. As with all materials, when concrete increases in temperature it will expand and when it decreases in temperature it will shrink. This expansion/shrinkage induces stress in the slab due to restraints such as friction with the bottom of the slab, stiffening ribs, piers etc.
External loads such as additional material or assemblies placed on top of the slab.

There are a number of measures that can be utilized to control re-entrant corner cracks including:

Contraction (Control) Joints: Place contraction joints at the re-entrant corner to create weak planes in the slab that will increase the possibility of cracks forming in the bottom of these contraction joints rather than at ~135° from the corner. Contraction joints can be formed by tooling the joints while the concrete is still plastic or with a saw after the concrete has set. It is important that contraction joints are placed as soon as possible before re-entrant corner cracks begin to form.
Construction Joints: Placing a construction joint 90° to the interior corner eliminates the re-entrant corner and thus the stress concentration.
Wet Curing. Wet curing of the slab will slow down the curing process and will create a more uniform cure rate between the top and bottom of the slab. This has the effect of reducing but not eliminating internal stresses. Wet curing can be accomplished by ponding the slab, utilizing foggers to maintain a humid environment on the slab, or by applying a chemical curing compound. In my experience, ponding of the slab is the most effective means of wet curing however it is typically the least practical.


Water to Cement Ratio: The primary ingredients in concrete are cement, water, fine aggregate and course aggregate. The water chemically reacts with the cement to bind the aggregate in a solid matrix. To fully hydrate cement, a water to cement ratio (w/c ) of 0.26 is required. Additional (free) water is added to the mix to increase the workability of the concrete. As more free water is added to the mix, it increases the shrinkage of the concrete because the free water will eventually evaporate out of the concrete. For our slab-on-grade design, Dudley Engineering typically specifies a maximum w/c ratio of 0.45. Additional workability can be achieved by adding water-reducing admixtures or superplasticizers to the mix.
Fly Ash: Fly ash is a recycled material that can be utilized in limited quantities to replace cement. Replacing a small portion of the cement with fly ash can have the benefit of reducing the expansion of the concrete during curing.
Concrete Additives: There are chemical admixtures which can be added to the concrete mix that reduce the shrinkage rate of the concrete. Recently, on a post-tensioned slab-on-grade foundation that was intended to remain exposed, Dudley Engineering specified a shrinkage-reducing admixture in the concrete. This, along with other measures listed above, has produced a slab that is showing no signs of visible cracks.
To have a slab-on-grade foundation that is relatively crack free even at re-entrant corners, a combination of the solutions addressed above should be utilized. In addition to having a more aesthetic slab, it will also exhibit better structural performance throughout the life of the structure.

Advanced Framing Techniques: Successful Utilization


In the pursuit of the infamous structural engineer T.Y. Lin’s powerful statement “To engineers who , rather than blindly following the codes of practice, seek to apply the laws of nature” I have always been interested in the subject of advanced framing techniques. The basic premise of advanced framing techniques is “a system of construction framing techniques designed to optimize building materials to produce wood-framed buildings with lower material and labor costs than conventional framed structures. Builders who utilize advanced framing techniques optimize framing material usage, reduce wood waste and, with effective insulation detailing, boost the building’s efficiency to meet today’s energy code requirements. When properly designed and constructed, advanced framed walls that are fully sheathed with wood structural panels, such as plywood or oriented strand board (OSB), provide the structural strength necessary to safely withstand the forces of nature.” (APA The Engineered Wood Association).

For professionals who have experience in structural steel and reinforced concrete framing systems, the definition of “advanced framing” will sound very similar to what has been the standard practice in steel and concrete for decades. The reason this practice is titled “advanced” in the wood industry is due to the wide use of prescriptive design, which has never been prevalent in the steel and concrete industries. It is my belief that the development of the prescriptive design in the International Residential Code has caused the wood framing industry to largely lag behind its counterparts in terms of material and labor efficiency. With the availability of software programs that can readily analyze wood framed structures I think it is time for the wood industry to re-evaluate the widespread use of prescriptive designs and utilize advanced framing techniques to elevate wood framing up to par with concrete and steel framing techniques.
I recently had the opportunity to put advanced framing techniques to the test with my own personal residence. My wife and I designed our 2,800 SF ranch house on our 10 acre property in Montgomery, Texas. For the framing, I designed all of the exterior walls to be 2×6 studs @ 24” O.C. The material savings came out to approximately 30% compared to traditional 2×4 stud walls @ 16” O.C. Other advanced framing techniques that were utilized included:
floor joists and rafters spaced @ 24” O.C. which took advantage of the the subfloor and roof deck’s inherent ability to span distance greater than 16” and reduced the total number of pieces.
Insulated exterior headers which reduced thermal bridging with little detriment to the structural capacity.
Blocking and straps at shear walls utilizing the “Force Transfer Around Openings” analysis approach that reduced the total length of shear walls required.

In the end, the framer was able to successfully implement the design as intended. Besides the material savings, the advanced framing techniques also provide additional benefits such as a larger cavity space for insulation in the exterior walls and less thermal bridging due to the reduced number of pieces in the exterior wall. I consider this implementation of advanced framing a success and look forward to its use on future projects.