# Knowledge Base

#### Why Dlubal Software?

• More than 45,000 users in 95 countries
• One software package for all application areas
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#### Wind Simulation & Wind Load Generation

With the stand-alone program RWIND Simulation, wind flows around simple or complex structures can be simulated by means of a digital wind tunnel.

The generated wind loads acting on these objects can be imported to RFEM or RSTAB.

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• ## ZPA Method in Response Spectrum Analysis

In a multi-modal response spectrum analysis, it is important to determine a sufficient number of eigenvalues of the structure and to consider their dynamic responses. Regulations such as EN 1998-1 [1] and other international standards require to activate 90 % of the structural mass. This means: to determine as many eigenvalues that the sum of the effective modal mass factor is greater 0.9.

• ## Determination of Pushover Curves

Pushover analysis is a nonlinear structural calculation for seismic analysis of structures. The load pattern is inferred from dynamic calculation of equivalent loads. These loads are incrementally increased until the global failure of the structure occurs. The nonlinear behaviour of a building is usually represented by using plastic hinges.

• ## Signed Results Using the Dominant Mode

In RF-/DYNAM Pro - Equivalent Loads, a signed result option in accordance to the dominant eigenmode is available since version X.06.3039. For the modal combination of results corresponding to the single eigenvalues a quadratic combination rule has to be used. In RFEM and RSTAB, the SRSS and the CQC rule are available. It is only allowed to combine results not loads directly. The reason are the mode shapes which are arbitrarly scaled and signed.

• ## Settings of the Time Course Monitor

The Time Course Monitor displays results of a time history analysis from RF‑/DYNAM Pro - Forced Vibrations. The graphic can be adjusted in the settings. This can be reached via the right click in the context menu. For example you can activate or deactivate the grid in the graphic. Those changes are overtaken into the printout report when you print the graphic.

• ## Quadratic Combination Using CQC Rule

In RF‑/DYNAM Pro - Equivalent Loads the CQC (Complete Quadratic Combination) rule is available since version X.06.3039.

• ## Complete Quadratic Combination (CQC) Rule

The CQC (Complete Quadratic Combination) rule is available in RFEM and RSTAB since version X.06.3039. In the General Data of the model you can activate the CQC rule and for Load Cases of type ‘Earthquake’ there are two new properties available, the ‘Angular frequency’ and the ‘Lehr's damping’.

• ## Considering Second-Order Theory in Dynamic Analysis

For the ultimate limit state design, EN 1998‑1 [1], Section 2.2.2 and 4.4.2.2, require the calculation considering the second‑order theory (P‑Δ effect). This effect need not be taken into account only if the interstorey drift sensitivity coefficient θ is less than 0.1. The coefficient θ is defined as follows:
$$\mathrm\theta\;=\;\frac{\displaystyle{\mathrm P}_\mathrm{tot}\;\cdot\;{\mathrm d}_\mathrm r}{{\mathrm V}_\mathrm{tot}\;\cdot\;\mathrm h}\;(1)$$
where
θ = interstorey drift sensitivity coefficient
Ptot = total gravity load at and above the storey considered in the seismic design situation (see Expression 2)
dr = design interstorey drift, evaluated as the difference of the average lateral displacements dS at the top and bottom of the storey under consideration; for this, the displacement is determined by using the linear design response spectrum with q = 1.0
Vtot = total seismic storey shear determined by using the linear design response spectrum
h = interstorey height

• ## Steady-state Solution for Periodically Excited Structures

With the modal analysis in DYNAM Pro - Forced Vibrations the steady-state solution can be determined for periodically excited structures. This is an advantage if only the steady state of the structure is of interest. Instead of the complete solution of the equation of motion, only the special solution is displayed.

• ## Neglecting Masses

Since version 5.06.1103 masses of nodes, lines, members and surfaces can be neglected in RF‑DYNAM Pro. The setting to activate this feature can be found in the Details dialogue, the neglected masses are valid for all defined mass cases.

• ## Time History Analysis of Explosion

With RF-DYNAM Pro - Forced Vibrations, you can perform a time history analysis. For example, you can analyse an explosion acting on a nearby building structure. In "Dynamik der Baukonstruktionen" by Christian Petersen, formulas for time diagrams and load distribution are described to specify an explosion. The picture shows the input of such an explosion load. In RFEM, free variable loads are available which enable flexible load distributions.

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#### First Steps

We provide hints and tips to help you get started with the main programs RFEM and RSTAB.

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