Frank E. Woeste

Reverse Proof Loading as a Means of Quality Control in Lumber Manufacturing

ABSTRACT THE determination of the strength distribution of a given structural grade of lumber from any chosen mill is of growing concern to the lumber industry. Lumber in the lower range of strength values is of prime interest. A reverse proof loading procedure, applied in bending, results in a more predictable product through elimination of the weak pieces resulting from imperfect performace of the visual stress rating model, variation in grader interpretation, and fluctuation in log quality. Experiments on 400 pieces of 2 by 4 No. 2 Dense KD Southern Pine involved loading 200 pieces to failure in bending and then reverse proof loading in bending the remaining 200 pieces. The pieces that survived the reverse proof loading were then tested to failure in bend-ing. Using a load and resistance reliability model, the probability of failure was calculated for the first 200 pieces (the control lumber). This then was compared to the probability of failure calculated with the resistance distribution of the reverse proof loaded lumber. The resistance distribution of the reverse proof loaded lumber data was then reduced in arbitrary steps and the pro-bability of failure recalculated. Results indicated that the reverse proof loading procedure could maintain the claimed allowable design value in the face of a 27 percent downward shift in the strength distribution within a grade.

Effect Of Span-Length On The Reliability Of Truss Bottom Chords

As input to the development of an LRFD specification for wood construction, seven truss patterns were studied to determine the impact of lower chord length on (conditional) probability of failure. The truss spans ranged from 5.59 m (18.33 ft) to 20.2 m (66.33 ft). The tensile properties of the lower chord were simulated using a lumber model that characterizes the serial correlation of tensile strength and modulus of elasticity (MOE) along 0.76 m (30 in.) segments of lumber. A companion value of bending strength for each piece of lower chord lumber was simulated based on the average MOE of the segments. Combined stress analysis was used to calculate the theoretical probability of failure of all the segments composing the lower chord. Based on the results and assumptions of the study, truss span length had no significant effect on the reliability of truss bottom chords. Also, truss pattern and lumber quality appear to have strong impacts on the reliability of bottom chords.

Rigid Roof Design for Post-Frame Buildings

Rigorous design methods are available to account for the effect of roof diaphragm action on post-frame buildings. These methods are computationally intensive and require sophisticated structural analysis software. This article presents a much simpler procedure for designing roof diaphragms based on the assumption that the roof diaphragm acts as an infinitely stiff, deep beam. The rigid roof method was compared with the more elaborate computer-based methods for a variety of building length-to-width ratios and diaphragm panel stiffnesses. Roof shear predictions were in good agreement with the results from the computer-based methods.

A probabilistic analysis of steel beam-columns

Abstract A probabilistic analysis of steel beam-columns in a typical medium rise office building designed in accordance with current AISC specifications was conducted. Risks were evaluated in terms of failure of probability for several failure modes and for various combinations of dead, live and wind loads. Effects of uncertainties in the resistance and the loads as well as modelling and prediction errors were included in the reliability analysis which is based on a first order second moment approach. Upper and lower bounds on the probability of failure of beam-columns were evaluated. Results obtained indicate the risk levels for the building considered.

Deck and Porch Floor Lateral Loading by Occupants

AbstractTwo deck floors, with different lateral stiffnesses, were constructed to measure lateral loads generated by occupants that are needed for design of residential or commercial exterior deck-type floors. Load was measured with two load cells attached at each end of the ledger representing the attachment to the building. The decks were supported on rollers, simulating minimal lateral resistance from columns. Occupants performed two different types of dynamic actions, in two orthogonal directions, at occupancy live load levels of 0.48, 0.96, 1.44, and 1.92 kPa (10, 20, 30, and 40 psf). The first loading cyclic was a side-to-side swaying motion that could result from a deliberate synchronized movement such as dancing. The second was an impulse-type load, which simulated horseplay-type activities. The difference in stiffness between the two decks resulted in a significant change in the human–structure interaction. Significant inertial effects were observed when the flexible deck was loaded parallel to th...

Lateral Load Path and Capacity of Exterior Decks

AbstractExterior decks must be designed to resist all applicable load cases. Vertical (gravity) loads are well defined, but less is known about designing decks for lateral loading. The focus of this study was to better understand the ultimate strength and load paths of two common deck constructions subjected to monotonic lateral loading. A portion of a conventional light-frame wood-floor diaphragm was built, to which the decks were attached. One deck was constructed with a lateral hold-down tension connector and the other deck had no hold-down tension connector. The lateral resistance and load path of each deck were investigated by applying a monotonic force through the centroid of the deck surface. The ledger board was connected to the house rim board with lag screws. Forces in each lag screw and hold-down connecting the deck to the diaphragm were recorded. Preliminary tests revealed a weakness in the deck joist–to–deck ledger connection; this was resolved by using joist hangers that featured a perpendic...

DEMONSTRATION OF WIND LOAD DESIGN FOR TIMBER FRAME STRUCTURES USING DIAPHRAGM ACTION

Current design procedures for timber frame structures that are enclosed by structural-insulated panels (SIPs) do not typically accommodate the contribution made by the SIPs in resisting lateral loads. However, post-frame building design procedures do include the diaphragm action of the metal cladding that encloses them, leading to more efficient structures. This investigation draws parallels between timber frame and post-frame structural systems and elucidates the appropriateness of the post-frame diaphragm design methods for contemporary timber frame buildings. A sample timber frame diaphragm design is performed and the parameters needed to effectively complete the design are identified.

A Simple Analysis Procedure for Calculating Post Forces

A method is presented to calculate post bending moments and axial forces in a post-frame building, subject to diaphragm action. This method uses the current design standard procedures outlined by ASAE EP 484.1 (1991a), but it eliminates the need for computer-based frame analyses. The method was validated for a large class of post-frame buildings with wall heights ranging from 3.05-6.10 m (10-20 ft) and length-to-width ratios less than 3.07. This method assumes that the posts are pinned connected to the truss, the truss is symmetric, and the posts are restrained at the groundline by a concrete floor.

Creep Deflection in Design of Metal Plate-Connected Wood Trusses

Creep deflection can be an important consideration in the design of metal plate–connected (MPC) wood trusses. Chapter 2 of the ANSI/TPI 1-2007 truss standard, referenced by the 2009 International Building Code (IBC), defines the responsibility of the registered design professional when specifying MPC wood trusses. Based on Section 2.3.2.4 (h) of the standard, the registered design professional shall provide design criteria that addresses in-service creep deflection behavior of flat roofs subject to ponding loads and floor trusses supporting stone or ceramic tile finishes. In this paper, we review relevant standards and research studies on creep behavior of MPC wood trusses and offer a rational calculation method based on 10- and 15-year test data for estimating creep deflection for parallel chord MPC wood trusses. Examples are included to illustrate the calculation method for determining a design creep factor that is related to the sustained load percentage relative to total design load. Some practical wa...

Reliability of multiple 2 X 4's used as truss lower chords.

ABSTRACT A procedure for investigating the relative safety of single and multiple lower chord member trusses is presented. The general approach is a Monte Carlo analysis using random strength parameters. A combina-tion of axial force and bending is considered and the reliability of the system is estimated in terms of a condi-tional probability of failure. The two different types of trusses analyzed are the glued plywood joint type and the metal plate type. Results indicate that differences in failure probabilities for the various cases are not signifi-cant and both single and double lower chord member trusses have about the same level of safety.