The ASCE 7-22 Standard [1], Sect. 12.9.1.6 specifies when P-delta effects should be considered when running a modal response spectrum analysis for seismic design. In the NBC 2020 [2], Sent. 4.1.8.3.8.c gives only a short requirement that sway effects due to the interaction of gravity loads with the deformed structure should be considered. Therefore, there may be situations where second-order effects, also known as P-delta, must be considered when carrying out a seismic analysis.
The National Building Code of Canada (NBC) 2020 Article 4.1.8.7 provides a clear procedure for earthquake methods of analysis. The more advanced method, the Dynamic Analysis Procedure in Article 4.1.8.12, should be used for all structure types except those that meet the criteria set forth in 4.1.8.7. The more simplistic method, the Equivalent Static Force Procedure (ESFP) in Article 4.1.8.11, can be used for all other structures.
The CSA S16:19 Stability Effects in Elastic Analysis method in Annex O.2 is an alternative option to the Simplified Stability Analysis Method in Clause 8.4.3. This article will describe the requirements of Annex O.2 and application in RFEM 6.
A standard scenario in timber member construction is the ability to connect smaller members by means of bearing on a larger girder member. Additionally, member end conditions may include a similar situation where the beam is bearing on a support type. In either scenario, the beam must be designed to consider the bearing capacity perpendicular to the grain according to NDS 2018 Sec. 3.10.2 and CSA O86:19 Clauses 6.5.6 and 7.5.9. In general structural design software, it is typically not possible to carry out this full design check, as the bearing area is unknown. However, in the new generation RFEM 6 and Timber Design add-on, the added 'design supports' feature now allows users to comply with the NDS and CSA bearing perpendicular to the grain design checks.
The AISC 360-16 steel standard requires stability consideration for a structure as a whole and each of its elements. Various methods for this are available, including direct consideration in the analysis, the effective length method, and the direct analysis method. This article will highlight the important requirements from Ch. C [1] and the direct analysis method to be incorporated in a structural steel model along with the application in RFEM 6.
Blast loads from high-energy explosives, either accidental or intentional, are rare but may be a structural design requirement. These dynamic loads differ from standard static loads due to their large magnitude and very short duration. A blast scenario can be carried out directly in an FEA program as a time history analysis to minimize loss of life and evaluate varying levels of structural damage.
Structure stability is not a new phenomenon when referring to steel design. The Canadian steel design standard CSA S16 and the most recent 2019 release are no exception. Detailed stability requirements can be addressed with either the Simplified Stability Analysis Method in Clause 8.4.3 or, new to the 2019 standard, the Stability Effects in Elastic Analysis method provided in Annex O.
The Aluminum Design Manual (ADM) 2020 was released in February 2020. The ADM 2020 gives guidance for both the allowable strength design (ASD) and load and resistance factor design (LRFD) for aluminum members to ensure reliability and safety for all aluminum structures. This latest standard was integrated in the RFEM/RSTAB add-on module RF-/ALUMINUM ADM. The text below will highlight the applicable updates relevant to the Dlubal programs.
The National Building Code of Canada (NBC) 2015 Article 4.1.8.7 provides a clear procedure for earthquake methods of analysis. The more advanced method, the Dynamic Analysis Procedure in Article 4.1.8.12, should be used for all structure types except those that meet the criteria set forth in 4.1.8.7. The more simplistic method, the Equivalent Static Force Procedure (ESFP) in Article 4.1.8.11, can be used for all other structures.
Reinforced concrete surface design for slabs, plates, and walls is possible in the RF-CONCRETE Surfaces module according to the ACI 318-19 or the CSA A23.3-19 standard. A common approach for slab design is the use of design strips for determining the average one-way internal forces over the width of the strip. This design strip method essentially takes a two-way slab element and applies a simpler one-way approach to determine the required reinforcement needed along the strip length.
The ASCE 7-16 standard requires both balanced and unbalanced snow load case scenarios for a structure's design consideration. While this may be more intuitive for flat or even gable/hip type roofs, the determination of snow loads is increasingly difficult for arch roofs due to complex geometry. However, with guidance from ASCE 7-16 on snow load calculations for curved roofs and RFEM's efficient load application tools, it is possible to consider both balanced and unbalanced snow loads for a reliable and safe structure design.
As gravity loads act on a structure, lateral displacement occurs. In turn, a secondary overturning moment is generated as the gravity load continues to act on the elements in the laterally displaced position. This effect is also known as "P-Delta (Δ)". Sec. 12.9.1.6 of the ASCE 7-16 Standard and the NBC 2015 Commentary specify when P-Delta effects should be considered during a modal response spectrum analysis.
The American Wood Council (AWC) has released the 2018 Edition of the National Design Specification (NDS) for Wood Construction. This is the second edition of the NDS to contain a chapter dedicated to cross-laminated timber (CLT) design. Therefore, a couple of revisions were included in the 2018 NDS when compared to the previous 2015 Edition.
When it comes to wind loads on building type structures as per ASCE 7, numerous resources can be found to supplement design standards and aid engineers with this lateral load application. However, engineers may find it more difficult to find similar resources for wind loading on non-building type structures. This article will examine the steps to calculate and apply wind loads as per ASCE 7-16 on a circular reinforced concrete tank with a dome roof.
Design loads specified in the AASHTO Bridge Design Specification are available in the RF-MOVE Surfaces moving load library. Design Truck (HS-20), Tandem, Type 3, and Overload are available options.
The Steel Joist Institute (SJI) previously developed Virtual Joist tables to estimate the section properties for Open Web Steel Joists. These Virtual Joist sections are characterized as equivalent wide-flange beams which closely approximate the joist chord area, effective moment of inertia, and weight. Virtual Joists are also available in the RFEM and RSTAB cross-section database.
After running an analysis in RF-/STEEL AISC, the mode shapes for sets of members can be viewed graphically in a separate window. Select the relevant set of members in the result window and click the [Mode Shapes] button.
If an aluminum member section is comprised of slender elements, failure can occur due to the local buckling of the flanges or webs before the member can reach full strength. In the add-on module RF-/ALUMINUM ADM, there are now three options for determining the nominal flexural strength for the limit state of local buckling, Mnlb, from Section F.3 in the 2015 Aluminum Design Manual. The three options include sections F.3.1 Weighted Average Method, F.3.2 Direct Strength Method, and F.3.3 Limiting Element Method.
In the AISC 360 – 14th Ed. C2.2, the direct analysis method requires initial imperfections to be taken into consideration. The important imperfection of recognition is column out-of-plumbness. According to C2.2a, the direct modeling of imperfections is one method to account for the effect of initial imperfections. However, in many situations, the expected displacements may not be known or easily predicted.
Requirements for the design of structural stability are given in the AISC 360 – 14th Ed. Chapter C. In particular, the direct analysis method provisions, previously located in Appendix 7 of the AISC 360 – 13th Ed., are described in detail. This method is considered an alternative to the effective length method, which in turn eliminates the need for effective length (K) factors other than 1.0.